feat(auth): authentication module with multi-tenant isolation (RFC-001)

Introduce an always-on auth layer with auto-created admin on first boot,
multi-tenant isolation for threads/stores, and a full setup/login flow.

Backend
- JWT access tokens with `ver` field for stale-token rejection; bump on
  password/email change
- Password hashing, HttpOnly+Secure cookies (Secure derived from request
  scheme at runtime)
- CSRF middleware covering both REST and LangGraph routes
- IP-based login rate limiting (5 attempts / 5-min lockout) with bounded
  dict growth and X-Forwarded-For bypass fix
- Multi-worker-safe admin auto-creation (single DB write, WAL once)
- needs_setup + token_version on User model; SQLite schema migration
- Thread/store isolation by owner; orphan thread migration on first admin
  registration
- thread_id validated as UUID to prevent log injection
- CLI tool to reset admin password
- Decorator-based authz module extracted from auth core

Frontend
- Login and setup pages with SSR guard for needs_setup flow
- Account settings page (change password / email)
- AuthProvider + route guards; skips redirect when no users registered
- i18n (en-US / zh-CN) for auth surfaces
- Typed auth API client; parseAuthError unwraps FastAPI detail envelope

Infra & tooling
- Unified `serve.sh` with gateway mode + auto dep install
- Public PyPI uv.toml pin for CI compatibility
- Regenerated uv.lock with public index

Tests
- HTTP vs HTTPS cookie security tests
- Auth middleware, rate limiter, CSRF, setup flow coverage

backend/docs/TITLE_GENERATION_IMPLEMENTATION.md

@@ -30,7 +30,7 @@
 
 ### 2. 配置文件
 
-#### [`config.yaml`](../config.yaml)
+#### [`config.yaml`](../../config.example.yaml)
 - ✅ 添加 title 配置段：
 ```yaml
 title:
@@ -51,7 +51,7 @@ title:
 - ✅ 故障排查指南
 - ✅ State vs Metadata 对比
 
-#### [`BACKEND_TODO.md`](../BACKEND_TODO.md)
+#### [`TODO.md`](TODO.md)
 - ✅ 添加功能完成记录
 
 ### 4. 测试