db: drizzle schema matching spec 02, initial migrations, settings service

Migration 0000 enables citext; 0001 creates all 39 tables. DB tests use a
throwaway database per file (TEST_DATABASE_URL, derived from .env in dev,
a postgres service in CI). Decision 0002: pg driver and @fastify/cookie.

Task: M1-T1

docs/spec/00-overview.md

@@ -160,6 +160,8 @@ AstDB keys (family/key). This list is complete; do not add keys without updating
 | WebSocket (api) | @fastify/websocket | latest |
 | Multipart uploads | @fastify/multipart | latest |
 | Rate limiting | @fastify/rate-limit | latest |
+| Cookies | @fastify/cookie | latest (decisions/0002) |
+| PostgreSQL driver | pg | latest (decisions/0002) |
 | QR codes | qrcode | latest |
 | Logging | pino | latest |
 | Tests | vitest | latest |