Docusaurus migration (#3343)

## Description of Changes

- Migrate the documentation site to **Docusaurus**.
- Add a **GitHub Action workflow** that runs `pnpm build` on pull
requests targeting `master`.
This command checks for broken links and images and ensures the site
builds correctly.
- Add a **GitHub Action workflow** to publish the docs automatically
when a merge occurs on the `docs/release` branch.

**Important**: The workflows haven't been tested yet due to the fact
that they need to be merged first before being able to run. It's a
fairly basic workflow I don't expect this to block anyone but anyways I
will make another PR with the complete changes when I can actually run
it.

---

## API and ABI Breaking Changes

No breaking changes for **SpacetimeDB** users.  
Documentation contributors should experience minimal disruption —
content is still written in Markdown.

---

## Expected Complexity Level and Risk

**Complexity:** 3/5

**Reasons:**
1. Several adjustments were made to fit Docusaurus conventions:
- Replaced our custom `:::server-rust` blocks with [Docusaurus `<Tabs/>`
components](https://docusaurus.io/docs/markdown-features/tabs).
- Converted “Note” callouts using
[admonitions](https://docusaurus.io/docs/markdown-features/admonitions)
instead of Markdown blockquotes.
- Updated all images (including Unity tutorial ones, which were
previously commented out).
- Moved images from the DO bucket into the repository at
`docs/static/images`.

2. Customized Docusaurus CSS and one component to apply our theme and
color palette.

---

## Testing

Tested locally.

---

## Review Notes

This PR involves many file changes — a full code review is likely not
productive.
Instead, please focus on verifying that the **documentation content**
was migrated correctly:

- Review sections you’re familiar with to confirm accuracy.
- Ensure formatting, links, and images render as expected.

You can follow the updated **README** for instructions on running
Docusaurus locally.

---------

Signed-off-by: Julien Lavocat <JulienLavocat@users.noreply.github.com>
Co-authored-by: John Detter <4099508+jdetter@users.noreply.github.com>
Co-authored-by: Tyler Cloutier <cloutiertyler@users.noreply.github.com>
Co-authored-by: = <cloutiertyler@gmail.com>

Author: 3 people

.github/workflows/docs-check-links.yml

@@ -0,0 +1,56 @@
+name: Docs / Publish
+
+permissions:
+  contents: read
+
+on:
+  push:
+    branches:
+      - docs/release
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: '22'
+      
+      - uses: pnpm/action-setup@v4
+        with:
+          run_install: true
+
+      - name: Get pnpm store directory
+        working-directory: sdks/typescript
+        shell: bash
+        run: |
+          echo "STORE_PATH=$(pnpm store path --silent)" >> $GITHUB_ENV
+
+      - uses: actions/cache@v4
+        name: Setup pnpm cache
+        with:
+          path: ${{ env.STORE_PATH }}
+          key: ${{ runner.os }}-pnpm-store-${{ hashFiles('**/pnpm-lock.yaml') }}
+          restore-keys: |
+            ${{ runner.os }}-pnpm-store-
+
+      - name: Install dependencies
+        working-directory: docs
+        run: pnpm install
+
+      - name: Docusaurus build
+        working-directory: docs
+        run: pnpm build
+
+      - name: Publish docs to S3
+        uses: shallwefootball/s3-upload-action@master
+        with:
+          aws_key_id: ${{ secrets.DOCS_AWS_KEY_ID }}
+          aws_secret_access_key: ${{ secrets.DOCS_AWS_SECRET_ACCESS_KEY}}
+          aws_bucket: spacetimedb-docs
+          source_dir: docs/build
+          destination_dir: 'docs'

.github/workflows/docs-publish.yaml

@@ -0,0 +1,44 @@
+name: Docs / Test
+permissions:
+  contents: read
+
+on:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: '22'
+      
+      - uses: pnpm/action-setup@v4
+        with:
+          run_install: true
+
+      - name: Get pnpm store directory
+        working-directory: sdks/typescript
+        shell: bash
+        run: |
+          echo "STORE_PATH=$(pnpm store path --silent)" >> $GITHUB_ENV
+
+      - uses: actions/cache@v4
+        name: Setup pnpm cache
+        with:
+          path: ${{ env.STORE_PATH }}
+          key: ${{ runner.os }}-pnpm-store-${{ hashFiles('**/pnpm-lock.yaml') }}
+          restore-keys: |
+            ${{ runner.os }}-pnpm-store-
+
+      - name: Install dependencies
+        working-directory: docs
+        run: pnpm install
+
+      - name: Docusaurus build
+        working-directory: docs
+        run: pnpm build

.github/workflows/docs-test.yaml

@@ -0,0 +1,16 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+[src/**.ts]
+indent_style = space
+indent_size = 2
+charset = utf-8
+trim_trailing_whitespace = true
+max_line_length = 120
+
+[*.json]
+indent_style = space
+indent_size = 2

.github/workflows/docs-validate-nav-build.yml

@@ -1,5 +1,20 @@
-**/.vscode
-.idea
-*.log
-node_modules
-.DS_store
+# Dependencies
+/node_modules
+
+# Production
+/build
+
+# Generated files
+.docusaurus
+.cache-loader
+
+# Misc
+.DS_Store
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*