docs: add CONTRIBUTING guide recommending codeyam-editor

New contributor guide: recommends making changes through codeyam-editor so
code, tests, and scenarios stay in sync, with the standard npm build/test/lint
workflow documented as the by-hand path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SYwMo8FrGx57SVf1BY96Qt

Author: jaredcosulich

CONTRIBUTING.md

@@ -0,0 +1,65 @@
+# Contributing
+
+Thanks for your interest in contributing! TabCommand is a Manifest V3 Chrome
+extension built with React and Vite, and developed with
+[codeyam-editor](https://codeyam.com) — the app's code and its runnable data
+**scenarios** are authored side by side against a live preview, and its test
+suite is captured and maintained as part of the same workflow.
+
+## The recommended workflow: codeyam-editor
+
+We strongly recommend making your change through codeyam-editor. It keeps the
+three things that have to stay in sync — code, tests, and scenarios — aligned
+automatically, so your change lands with its scenarios captured and its tests
+registered instead of drifting apart over time.
+
+```bash
+# Clone the repo
+git clone https://github.com/codeyam-ai/tabcommand && cd tabcommand
+
+# Install codeyam-editor
+npm install -g @codeyam-editor/codeyam-editor@latest
+
+# Launch the editor (split-screen terminal + live preview)
+codeyam-editor editor
+```
+
+codeyam-editor requires a subscription to Claude, Gemini, or Codex. Inside the
+editor you describe or make a change and it walks you through capturing the
+scenarios and tests that cover it, so nothing you contribute goes untested or
+unillustrated.
+
+## Building and testing by hand
+
+If you're working without the editor, the standard workflow is fully supported.
+Requires Node.js 22+.
+
+```bash
+# Install dependencies
+npm install
+
+# Run the test suite and the linter
+npm test
+npm run lint
+
+# Build the extension
+npm run build
+```
+
+To try your build in Chrome: open `chrome://extensions`, enable **Developer
+mode**, choose **Load unpacked**, and select the `build/` folder. After code
+changes, re-run `npm run build` and reload the extension to pick them up.
+
+## Pull requests
+
+1. Fork and create a topic branch off `main`.
+2. Make your change — ideally in codeyam-editor, so its scenarios and tests are
+   captured and registered as you go.
+3. Ensure `npm test`, `npm run lint`, and `npm run build` all pass.
+4. Open a PR describing what changed and why.
+
+## Code of conduct
+
+Please keep interactions respectful and constructive; by participating you
+agree to help keep this a welcoming community. To report a security issue, see
+[SECURITY.md](SECURITY.md).