docs: split CLAUDE.md into focused reference files

Move Common Commands to docs/COMMANDS.md and add docs/CONVENTIONS.md
for frontend patterns (SWR, filters, Mantine, routing, API URLs).
CLAUDE.md now only contains runtime rules and pointers.

CLAUDE.md

@@ -13,31 +13,9 @@ Default to Bun instead of Node.js everywhere:
 - `bunx <pkg>` not `npx`
 - Bun auto-loads `.env` — never use dotenv.
 
-## Common Commands
+## Commands
 
-```bash
-bun run dev          # dev server with hot reload (bun --watch src/serve.ts)
-bun run build        # Vite production build
-bun run start        # production server (NODE_ENV=production)
-bun run typecheck    # tsc --noEmit
-bun run lint         # biome check src/
-bun run lint:fix     # biome check --write src/
-
-# Database
-bun run db:migrate   # prisma migrate dev
-bun run db:seed      # seed demo data
-bun run db:generate  # regenerate prisma client
-bun run db:studio    # Prisma Studio GUI
-bun run db:push      # push schema without migration
-
-# Tests
-bun run test              # all tests
-bun run test:unit         # tests/unit/
-bun run test:integration  # tests/integration/ — no server needed
-bun run test:e2e          # tests/e2e/ — requires Lightpanda Docker
-```
-
-Run a single test file: `bun test tests/integration/auth.test.ts`
+See @docs/COMMANDS.md
 
 ## Architecture
 
@@ -50,3 +28,7 @@ See @docs/TESTING.md
 ## Dev Tools
 
 See @docs/DEV_TOOLS.md
+
+## Frontend Conventions
+
+See @docs/CONVENTIONS.md