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/packages/harness/deerflow/config/paths.py

@@ -9,6 +9,12 @@ VIRTUAL_PATH_PREFIX = "/mnt/user-data"
 _SAFE_THREAD_ID_RE = re.compile(r"^[A-Za-z0-9_\-]+$")
 
 
+def _default_local_base_dir() -> Path:
+    """Return the repo-local DeerFlow state directory without relying on cwd."""
+    backend_dir = Path(__file__).resolve().parents[4]
+    return backend_dir / ".deer-flow"
+
+
 def _validate_thread_id(thread_id: str) -> str:
     """Validate a thread ID before using it in filesystem paths."""
     if not _SAFE_THREAD_ID_RE.match(thread_id):
@@ -67,8 +73,7 @@ class Paths:
     BaseDir resolution (in priority order):
         1. Constructor argument `base_dir`
         2. DEER_FLOW_HOME environment variable
-        3. Local dev fallback: cwd/.deer-flow  (when cwd is the backend/ dir)
-        4. Default: $HOME/.deer-flow
+        3. Repo-local fallback derived from this module path: `{backend_dir}/.deer-flow`
     """
 
     def __init__(self, base_dir: str | Path | None = None) -> None:
@@ -104,11 +109,7 @@ class Paths:
         if env_home := os.getenv("DEER_FLOW_HOME"):
             return Path(env_home).resolve()
 
-        cwd = Path.cwd()
-        if cwd.name == "backend" or (cwd / "pyproject.toml").exists():
-            return cwd / ".deer-flow"
-
-        return Path.home() / ".deer-flow"
+        return _default_local_base_dir()
 
     @property
     def memory_file(self) -> Path: