[claude] Add CONTRIBUTING.md for the-nexus (#284) (#311)

Co-authored-by: Claude (Opus 4.6) <claude@hermes.local>
Co-committed-by: Claude (Opus 4.6) <claude@hermes.local>

CONTRIBUTING.md

@@ -0,0 +1,62 @@
+# Contributing to The Nexus
+
+Thanks for contributing to Timmy's sovereign home. Please read this before opening a PR.
+
+## Project Stack
+
+- Vanilla JS ES modules, Three.js 0.183, no bundler
+- Static files — no build step
+- Import maps in `index.html` handle Three.js resolution
+
+## Architecture
+
+```
+index.html    # Entry point: HUD, chat panel, loading screen
+style.css     # Design system: dark space theme, holographic panels
+app.js        # Three.js scene, shaders, controls, game loop (~all logic)
+```
+
+Keep logic in `app.js`. Don't split without a good reason.
+
+## Conventions
+
+- **ES modules only** — no CommonJS, no bundler imports
+- **Color palette** — defined in `NEXUS.colors` at the top of `app.js`; use it, don't hardcode colors
+- **Conventional commits**: `feat:`, `fix:`, `refactor:`, `test:`, `chore:`
+- **Branch naming**: `claude/issue-{N}` for agent work, `yourname/issue-{N}` for humans
+- **One PR at a time** — wait for the merge-bot before opening the next
+
+## Before You Submit
+
+1. Run the JS syntax check:
+   ```bash
+   node --check app.js
+   ```
+2. Validate `index.html` — it must be valid HTML
+3. Keep JS files under 500 KB
+4. Any `.json` files you add must parse cleanly
+
+These are the same checks the merge-bot runs. Failing them will block your PR.
+
+## Running Locally
+
+```bash
+npx serve . -l 3000
+# open http://localhost:3000
+```
+
+## PR Rules
+
+- Base your branch on latest `main`
+- Squash merge only
+- **Do not merge manually** — the merge-bot handles merges
+- If merge-bot comments "CONFLICT": rebase onto `main` and force-push your branch
+- Include `Fixes #N` or `Refs #N` in your commit message
+
+## Issue Ordering
+
+The Nexus v1 issues are sequential — each builds on the last. Check the build order in [CLAUDE.md](CLAUDE.md) before starting work to avoid conflicts.
+
+## Questions
+
+Open an issue or reach out via the Timmy Terminal chat inside the Nexus.