docs: add local development and testing to maintainer's guide (#77)

* docs: add local development & testing guide

Document how maintainers run the test suite (make targets) and load the
plugin locally in Claude Code (claude --plugin-dir) and Cursor (make
cursor-install), and cross-reference it from the Releases step that already
assumes tests are run locally.

* docs: simplify setup sentence to venv + deps

* docs: genericize test descriptions away from Ollama specifics

* docs: refine testing section wording and .env setup steps

* docs: block-format the `claude plugin validate` command

Applies Eden's suggestion from PR #77 review.

Co-authored-by: Eden Zimbelman <18134219+zimeg@users.noreply.github.com>

* docs: add Cursor to the tools list

Responds to Eden's question on PR #77 — Cursor is a supported alternative
to Claude Code for verifying skills locally.

---------

Co-authored-by: Eden Zimbelman <18134219+zimeg@users.noreply.github.com>

Author: mwbrooks

.github/maintainers_guide.md

@@ -13,6 +13,8 @@ Maintaining this repo requires:
 - **[Claude Code][claude-code]**: the primary development and maintenance tool.
   Most tasks (authoring skills, reviewing diffs) are performed through Claude
   Code rather than traditional CLI tooling.
+- **[Cursor][cursor]**: an alternative agentic coding environment. Useful for
+  verifying that skills and commands work outside Claude Code before release.
 - **Git**: standard version control.
 - **[GitHub CLI (`gh`)][gh-cli]**: for creating PRs as drafts and managing
   issues.
@@ -44,6 +46,83 @@ source .venv/bin/activate
 
 ---
 
+## Local Development & Testing
+
+Before you release (or open a PR), exercise your changes locally: run the test
+suite, and load the plugin into Claude Code or Cursor to try the skills and
+commands by hand.
+
+### Setup
+
+Run the one-time setup, which creates the virtualenv and installs the test and
+lint dependencies (requires Python 3.14+, see above):
+
+```sh
+make install
+```
+
+The tests read configuration from environment variables. Copy the example file
+and fill in what you need — each variable is documented inline, and the
+`Makefile` auto-loads `.env`:
+
+```sh
+cp .env.example .env
+vim .env
+# Set the environment variables
+```
+
+### Running the tests
+
+Always use the `make` targets — never invoke `pytest`, `ruff`, or `python`
+directly. The targets manage the virtualenv, load `.env`, and set up the test
+dependencies for you.
+
+```sh
+make test-unit   # fast structural + frontmatter checks (this is what CI runs)
+make test-eval   # LLM-judged skill evaluations (local only)
+make test        # both
+make lint        # Ruff linter (line-length 120)
+make format      # Ruff auto-format + fix
+```
+
+### Testing in Claude Code
+
+Load your local changes into Claude Code for a single session with the
+`--plugin-dir` flag:
+
+```sh
+claude --plugin-dir ./
+```
+
+This loads the `slack` plugin from your checkout — its skills and commands, and
+the HTTP MCP server from `.mcp.json`. If you already have the published
+`slack` plugin installed, the local copy takes precedence **for that session
+only**: nothing is written to your settings, and the installed version is
+untouched when you exit. After editing a skill or command, run `/reload-plugins`
+inside the session to pick up the change without restarting.
+
+Check the plugin's structure without launching a session:
+
+```sh
+claude plugin validate
+```
+
+### Testing in Cursor
+
+Install the plugin into your local Cursor, then reload plugins in Cursor to pick
+up the changes:
+
+```sh
+make cursor-install
+```
+
+This copies the plugin into `~/.cursor/plugins/slack@local` and registers it.
+
+To remove it, run `make cursor-uninstall`. (`make clean` also runs the Cursor
+uninstall, in addition to removing the virtualenv and other generated files.)
+
+---
+
 ## Versioning
 
 Follow the [conventional commit specification][conv-commits]. PR titles and commit messages use prefixes like `feat:`, `fix:`, `chore:`, `docs:`, etc. First letter after the prefix is lowercase unless it's a proper noun.
@@ -80,7 +159,7 @@ Releasing can feel intimidating at first, but don't fret! Venture on!
 
 New official package versions are published when the release PR created from changesets is merged. Follow these steps to build confidence:
 
-1. **Run the tests locally**: Before merging the release PR please run all the tests especially the eval ones. If they no longer pass we may need fix it before releasing the changes.
+1. **Run the tests locally**: Before merging the release PR please run all the tests (see [Local Development & Testing](#local-development--testing)), especially the eval ones. If they no longer pass we may need fix it before releasing the changes.
 
 2. **Check GitHub**: Please check if issues or pull requests are still open either decide to postpone the release or save those changes for a future update.
 
@@ -123,6 +202,7 @@ Patch and minor updates are auto-approved and auto-merged via the
 ---
 
 [claude-code]: https://claude.ai/code
+[cursor]: https://cursor.com
 [gh-cli]: https://cli.github.com
 [conv-commits]: https://www.conventionalcommits.org
 [semver]: https://semver.org