Add CLAUDE.md (#479)

* add CLAUDE.md

* update testing guidelines

CLAUDE.md

@@ -0,0 +1,28 @@
+# Development Guidelines for Stack Auth
+
+## Build/Test/Lint Commands
+- Build: `pnpm build` (all), `pnpm build:packages` (packages only), `pnpm build:backend` (backend)
+- Lint: `pnpm lint` (zero warnings allowed)
+- Typecheck: `pnpm typecheck`
+- Test: `pnpm test` (all), `pnpm test:unit` (unit tests), `pnpm test:e2e` (e2e tests)
+- Run single test: `pnpm test path/to/test.test.ts` or `pnpm test -t "test name pattern"`
+- Start dependencies: `pnpm start-deps` (DB, services), `pnpm stop-deps` (shutdown)
+- Dev mode: `pnpm dev` (all services) or `pnpm dev:basic` (backend+dashboard)
+
+## Coding Guidelines
+- TypeScript with strict types, prefer `type` over `interface`
+- 2-space indentation, spaces in braces, semicolons required
+- Return promises with `return await`, no floating promises
+- Proper error handling for async code with try/catch
+- Use helper functions: `yupXyz()` for validation, `getPublicEnvVar()` for env
+- Switch cases must use blocks
+- React Server Components preferred where applicable
+- No direct 'use' imports from React (use React.use instead)
+- Follow existing file structure and naming patterns
+
+## Testing Guidelines
+- Import test utilities from `/apps/e2e/test/helpers.ts`
+- Prefer inline snapshot testing with `expect(response).toMatchInlineSnapshot(...)`
+
+## Monorepo Structure
+Managed with Turbo and pnpm workspaces. Core packages in `packages/`, apps in `apps/`.