feat: auth middleware, brain data layer, Valkey queue (P1-002, P1-003, P1-004)

Auth middleware (P1-002):
- DatabaseModule provides Db instance with graceful shutdown
- AuthModule mounts BetterAuth at /api/auth/* via toNodeHandler
- AuthGuard validates sessions via BetterAuth API
- CurrentUser decorator extracts user from request

Brain data layer (P1-003):
- CRUD repositories for projects, missions, tasks, conversations
- createBrain(db) factory returns all repositories
- Re-exports drizzle-orm query helpers from @mosaic/db to avoid
  duplicate package resolution

Queue (P1-004):
- ioredis-based Valkey client with createQueue/createQueueClient
- Enqueue/dequeue, pub/sub, queue length operations

Closes #11, Closes #12, Closes #13

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/db/src/index.ts

@@ -1,3 +1,4 @@
 export { createDb, type Db, type DbHandle } from './client.js';
 export { runMigrations } from './migrate.js';
 export * from './schema.js';
+export { eq, and, or, desc, asc, sql, inArray, isNull, isNotNull } from 'drizzle-orm';