chore(license): dual-license — Apache-2.0 SDK, MPL-2.0 engine; add CLA scaffold (#95)

Split licensing so third parties can build proprietary plugins (Apache-2.0 on
pj_base + pj_plugins) while the storage engine stays weak copyleft (MPL-2.0 on
pj_datastore). Adds per-file SPDX headers, the full Apache-2.0 and MPL-2.0
texts, a per-module LICENSE map, and updates conanfile.py (license =
"Apache-2.0 AND MPL-2.0") and the README.

Also scaffolds a CLA Assistant Lite workflow (.github/workflows/cla.yml) and
CLA.md, whose relicensing grant preserves a future commercial-license option
for the engine. The workflow is inert until enabled (see CLA.md setup notes).

Co-authored-by: Davide Faconti <dfaconti@aurynrobotics.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 3 people

.github/workflows/cla.yml

@@ -0,0 +1,60 @@
+name: CLA Assistant
+
+# CLA Assistant Lite (contributor-assistant/github-action).
+#
+# On every pull request, the bot checks whether each contributor has signed the
+# CLA in CLA.md. Unsigned contributors are asked to sign by posting a comment on
+# their PR with the exact phrase:
+#
+#     I have read the CLA Document and I hereby sign the CLA
+#
+# Signatures are appended to a JSON file (path-to-signatures) committed to the
+# `branch` configured below. Posting `recheck` re-runs the check.
+#
+# ── One-time setup ────────────────────────────────────────────────────────────
+#   1. The `branch` used to store signatures MUST exist and MUST NOT be branch-
+#      protected (the bot pushes directly to it). Create it once:
+#         git branch cla-signatures && git push -u origin cla-signatures
+#   2. If you store signatures in the same repo on an UNPROTECTED branch, the
+#      built-in GITHUB_TOKEN is enough. PERSONAL_ACCESS_TOKEN is only required
+#      when storing signatures in a *remote* repo, or when the storage branch is
+#      protected. If needed, add a repo-scoped PAT as the secret
+#      PERSONAL_ACCESS_TOKEN in Settings → Secrets and variables → Actions.
+#   3. Edit `allowlist` below to include maintainers and bots (they skip the CLA).
+
+on:
+  issue_comment:
+    types: [created]
+  pull_request_target:
+    types: [opened, synchronize, closed]
+
+permissions:
+  actions: write
+  contents: write
+  pull-requests: write
+  statuses: write
+
+jobs:
+  cla-assistant:
+    runs-on: ubuntu-latest
+    steps:
+      - name: CLA Assistant
+        if: >-
+          (github.event.comment.body == 'recheck'
+            || github.event.comment.body == 'I have read the CLA Document and I hereby sign the CLA')
+          || github.event_name == 'pull_request_target'
+        uses: contributor-assistant/github-action@v2.6.1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          # PERSONAL_ACCESS_TOKEN: ${{ secrets.PERSONAL_ACCESS_TOKEN }}  # only for remote/protected storage
+        with:
+          path-to-document: 'https://github.com/PlotJuggler/plotjuggler_core/blob/development/CLA.md'
+          path-to-signatures: 'signatures/version1/cla.json'
+          branch: 'cla-signatures'
+          allowlist: facontidavide,bot*,*[bot]
+          custom-notsigned-prcomment: >-
+            Thank you for your contribution. Before we can merge it, please sign the
+            [Contributor License Agreement](https://github.com/PlotJuggler/plotjuggler_core/blob/development/CLA.md)
+            by posting a comment on this pull request with exactly the text below:
+          custom-pr-sign-comment: 'I have read the CLA Document and I hereby sign the CLA'
+          custom-allsigned-prcomment: 'All contributors have signed the CLA. Thank you!'

CLA.md

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+<!--
+  TEMPLATE — REVIEW BEFORE ENABLING THE CLA WORKFLOW.
+  This Contributor License Agreement was drafted as a starting point and is not
+  legal advice. Have it reviewed by a lawyer before relying on it, especially the
+  relicensing grant in Section 2, which is what preserves the option to offer
+  pj_datastore under commercial terms. Once contributors begin signing, changing
+  the terms requires re-collecting signatures, so settle the wording first.
+-->
+
+# PlotJuggler Core — Individual Contributor License Agreement
+
+Thank you for contributing to PlotJuggler Core (the "Project"). This Contributor
+License Agreement ("Agreement") sets out the terms under which You provide
+Contributions to the Project. It protects You, the Project, and downstream users
+by making the intellectual-property terms of Your Contributions explicit.
+
+By signing this Agreement (see "How to sign" below) You accept and agree to these
+terms for Your past, present, and future Contributions to the Project.
+
+## 1. Definitions
+
+- **"You"** (or **"Your"**) means the individual who submits a Contribution, or
+  the legal entity on whose behalf the Contribution is submitted.
+- **"Project Owner"** means Davide Faconti, the maintainer and copyright holder
+  of PlotJuggler Core, and any successor maintainer or assignee.
+- **"Contribution"** means any original work of authorship, including any
+  modification of or addition to existing work, that You intentionally submit to
+  the Project (e.g. via pull request, patch, or issue attachment) for inclusion
+  in or documentation of the Project.
+
+## 2. Copyright License
+
+You grant the Project Owner and recipients of software distributed by the Project
+a **perpetual, worldwide, non-exclusive, royalty-free, irrevocable** copyright
+license to reproduce, prepare derivative works of, publicly display, publicly
+perform, **sublicense, relicense, and distribute** Your Contributions and such
+derivative works.
+
+You expressly agree that the Project Owner may **license and distribute Your
+Contributions under any license terms, including open-source, proprietary, and
+commercial terms** (for example, dual-licensing the storage engine). This right
+to relicense survives even if the Project's default license changes. You retain
+all right, title, and interest in Your Contributions not expressly granted here,
+including the right to use them for any other purpose.
+
+## 3. Patent License
+
+You grant the Project Owner and recipients of software distributed by the Project
+a perpetual, worldwide, non-exclusive, royalty-free, irrevocable (except as
+stated below) patent license to make, have made, use, offer to sell, sell,
+import, and otherwise transfer Your Contributions, where such license applies
+only to those patent claims licensable by You that are necessarily infringed by
+Your Contribution alone or by combination of Your Contribution with the Project.
+
+If any entity institutes patent litigation alleging that Your Contribution, or
+the Project to which You contributed, constitutes direct or contributory patent
+infringement, then any patent licenses granted to that entity under this
+Agreement for that Contribution terminate as of the date such litigation is
+filed.
+
+## 4. Moral Rights
+
+To the fullest extent permitted by applicable law, You waive, and agree not to
+assert, any moral rights in Your Contributions against the Project Owner or
+downstream recipients.
+
+## 5. Your Representations
+
+You represent that:
+
+1. Each Contribution is either Your original creation, or You have sufficient
+   rights to submit it under the terms of this Agreement.
+2. The grants above do not violate any agreement You have with a third party. If
+   Your employer has rights to intellectual property You create, You represent
+   that You have received permission to make the Contributions on behalf of that
+   employer, or that the employer has waived such rights for Your Contributions.
+3. You are not aware of any third-party rights that would make the grants in this
+   Agreement inaccurate, and You will notify the Project Owner if You later become
+   aware of any such rights.
+
+## 6. No Warranty / No Obligation
+
+Unless required by applicable law or agreed to in writing, You provide Your
+Contributions "AS IS", without warranties or conditions of any kind. The Project
+Owner is under no obligation to accept, use, or distribute any Contribution.
+
+## How to sign
+
+To sign this Agreement, post a comment on your pull request containing exactly:
+
+> I have read the CLA Document and I hereby sign the CLA
+
+The automated CLA Assistant records your signature against your GitHub username.
+If you are contributing on behalf of a company, ensure you are authorized to do
+so before signing.

LICENSE

@@ -1,21 +1,26 @@
-MIT License
+PlotJuggler Core is licensed per-module. Every source file carries an
+SPDX-License-Identifier header that is authoritative for that file.
 
-Copyright (c) 2026 Davide Faconti
+  Module          License        Full text
+  ------------    -----------    ---------------
+  pj_base         Apache-2.0     LICENSE-APACHE
+  pj_plugins      Apache-2.0     LICENSE-APACHE
+  examples        Apache-2.0     LICENSE-APACHE
+  pj_datastore    MPL-2.0        LICENSE-MPL
+
+Rationale:
 
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
+  - The plugin-facing surface (pj_base, pj_plugins) is Apache-2.0 so that
+    third parties may build proprietary plugins and applications on top of
+    the SDK without restriction. Apache-2.0 also grants an explicit patent
+    license to downstream users.
 
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
+  - The storage engine (pj_datastore) is MPL-2.0. MPL-2.0 is file-level
+    (weak) copyleft: modifications to the engine's own source files must be
+    published, but the engine may be combined with proprietary code and
+    linked into proprietary applications.
 
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
+Plugins load through a stable C ABI and never statically link pj_datastore,
+so the MPL-2.0 engine imposes no obligations on plugin authors.
+
+Copyright (c) 2026 Davide Faconti