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/brain/src/index.ts

@@ -1 +1,22 @@
-export const VERSION = '0.0.0';
+export { createBrain, type Brain } from './brain.js';
+export {
+  createProjectsRepo,
+  type ProjectsRepo,
+  type Project,
+  type NewProject,
+} from './projects.js';
+export {
+  createMissionsRepo,
+  type MissionsRepo,
+  type Mission,
+  type NewMission,
+} from './missions.js';
+export { createTasksRepo, type TasksRepo, type Task, type NewTask } from './tasks.js';
+export {
+  createConversationsRepo,
+  type ConversationsRepo,
+  type Conversation,
+  type NewConversation,
+  type Message,
+  type NewMessage,
+} from './conversations.js';