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/app/gateway/auth/config.py

@@ -0,0 +1,55 @@
+"""Authentication configuration for DeerFlow."""
+
+import logging
+import os
+import secrets
+
+from dotenv import load_dotenv
+from pydantic import BaseModel, Field
+
+load_dotenv()
+
+logger = logging.getLogger(__name__)
+
+
+class AuthConfig(BaseModel):
+    """JWT and auth-related configuration. Parsed once at startup."""
+
+    jwt_secret: str = Field(
+        ...,
+        description="Secret key for JWT signing. MUST be set via AUTH_JWT_SECRET.",
+    )
+    token_expiry_days: int = Field(default=7, ge=1, le=30)
+    users_db_path: str | None = Field(
+        default=None,
+        description="Path to users SQLite DB. Defaults to .deer-flow/users.db",
+    )
+    oauth_github_client_id: str | None = Field(default=None)
+    oauth_github_client_secret: str | None = Field(default=None)
+
+
+_auth_config: AuthConfig | None = None
+
+
+def get_auth_config() -> AuthConfig:
+    """Get the global AuthConfig instance. Parses from env on first call."""
+    global _auth_config
+    if _auth_config is None:
+        jwt_secret = os.environ.get("AUTH_JWT_SECRET")
+        if not jwt_secret:
+            jwt_secret = secrets.token_urlsafe(32)
+            os.environ["AUTH_JWT_SECRET"] = jwt_secret
+            logger.warning(
+                "⚠ AUTH_JWT_SECRET is not set — using an auto-generated ephemeral secret. "
+                "Sessions will be invalidated on restart. "
+                "For production, add AUTH_JWT_SECRET to your .env file: "
+                'python -c "import secrets; print(secrets.token_urlsafe(32))"'
+            )
+        _auth_config = AuthConfig(jwt_secret=jwt_secret)
+    return _auth_config
+
+
+def set_auth_config(config: AuthConfig) -> None:
+    """Set the global AuthConfig instance (for testing)."""
+    global _auth_config
+    _auth_config = config