docs: add CONTRIBUTING.md

[interacsean]

Summary

• Adds CONTRIBUTING.md documenting the end-to-end contributor lifecycle (issue → branch → develop → quality-check → changeset → PR → review → release), sourced from a previously-drafted (stashed) version.
• Updated the draft to match current repo state:
  • Added the check-licenses CI workflow (introduced in ci: add check-licenses workflow #353) to the CI table and CI/CD workflow reference.
  • Added the now in-repo api-design-review skill (.agents/skills/api-design-review/) alongside the existing Copilot prompt.
  • Removed the /board-issue command reference — that's a personal Claude Code skill some contributors have installed locally, not something checked into this repo, so the doc now describes filing on the project board generically instead.

Test plan

• pnpm exec oxfmt --check CONTRIBUTING.md passes
• Team reviews wording/accuracy of the workflow description

[IzumiSy]

Overall this looks good, but how do we manage the relationship between this and CLAUDE.md?

Some information looks overlapped

[interacsean]

Yep good point. We should have CLAUDE.md refer to CONTRIBUTING.md as an include so it is ensured to be read. I think a more human-friendly CONTRIBUTING is useful, as I did not find all the processes clear and intuitive when I came back to work on AppShell a few weeks ago

[interacsean]

Thanks both — re-evaluated based on the common thread across these comments: the doc was re-documenting mutable rules (add-component's house rules, quality-check's procedure, CI trigger mechanics, four reference tables) that live authoritatively elsewhere, and it had already drifted as a result — the CI table said push when ci-packages.yaml/ci-e2e.yaml are actually pull_request-triggered, and the e2e env var list was missing VITE_TAILOR_AI_GATEWAY_URL.

Pushed a trim (7ed1d16) that keeps the narrative/lifecycle framing but replaces every restated rule/table with a pointer to its source of truth (.agents/skills/**, .github/workflows/, etc.) so there's exactly one place to update per convention. Also linked CLAUDE.md → CONTRIBUTING.md per @interacsean's comment, so coding agents are guaranteed to load it.

[IzumiSy]

One more last thing: I found README.md also has mention to development setup, so let's trim that all out, and just add a link to CONTRIBUTION.md.

app-shell/README.md

Lines 30 to 71 in 78b182b

	## Development
	This project is a monorepo managed with pnpm.
	### Prerequisites
	This project requires **Node.js 24** (see `engines` in `package.json`; CI runs on Node 24). Some build tooling (`tsdown`) relies on Node 24's native TypeScript config loading — on older versions it falls back to a loader that isn't installed, and the build fails. `engine-strict` is enabled, so `pnpm install` will refuse to run on an unsupported version.
	If you use [nvm](https://github.com/nvm-sh/nvm), a `.nvmrc` is provided:
	```bash
	nvm use # or: nvm install
	```
	### Setup
	```bash
	pnpm install
	```
	### Commands
	```bash
	pnpm dev # Start all packages in development mode with hot reloading
	pnpm build # Build all packages for production
	pnpm type-check # Run type checking across all packages
	```
	### Testing
	```bash
	cd packages/core && pnpm test
	```
	### Publishing
	This project uses [changesets](https://github.com/changesets/changesets) for version management:
	```bash
	pnpm changeset:create # Create a changeset describing your changes
	pnpm changeset:publish # Build and publish to NPM (automated via CI)
	```