feat: Stage 1 — backend and frontend scaffolding

Backend (tasks 1.1, 1.5–1.8):
- pyproject.toml with FastAPI, Pydantic v2, aiosqlite, APScheduler 3.x,
  structlog, bcrypt; ruff + mypy strict configured
- Pydantic Settings (BANGUI_ prefix env vars, fail-fast validation)
- SQLite schema: settings, sessions, blocklist_sources, import_log;
  WAL mode + foreign keys; idempotent init_db()
- FastAPI app factory with lifespan (DB, aiohttp session, scheduler),
  CORS, unhandled-exception handler, GET /api/health
- Fail2BanClient: async Unix-socket wrapper using run_in_executor,
  custom error types, async context manager
- Utility modules: ip_utils, time_utils, constants
- 47 tests; ruff 0 errors; mypy --strict 0 errors

Frontend (tasks 1.2–1.4):
- Vite + React 18 + TypeScript strict; Fluent UI v9; ESLint + Prettier
- Custom brand theme (#0F6CBD, WCAG AA contrast) with light/dark variants
- Typed fetch API client (ApiError, get/post/put/del) + endpoints constants
- tsc --noEmit 0 errors

backend/app/models/auth.py

@@ -0,0 +1,46 @@
+"""Authentication Pydantic models.
+
+Request, response, and domain models used by the auth router and service.
+"""
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class LoginRequest(BaseModel):
+    """Payload for ``POST /api/auth/login``."""
+
+    model_config = ConfigDict(strict=True)
+
+    password: str = Field(..., description="Master password to authenticate with.")
+
+
+class LoginResponse(BaseModel):
+    """Successful login response.
+
+    The session token is also set as an ``HttpOnly`` cookie by the router.
+    This model documents the JSON body for API-first consumers.
+    """
+
+    model_config = ConfigDict(strict=True)
+
+    token: str = Field(..., description="Session token for use in subsequent requests.")
+    expires_at: str = Field(..., description="ISO 8601 UTC expiry timestamp.")
+
+
+class LogoutResponse(BaseModel):
+    """Response body for ``POST /api/auth/logout``."""
+
+    model_config = ConfigDict(strict=True)
+
+    message: str = Field(default="Logged out successfully.")
+
+
+class Session(BaseModel):
+    """Internal domain model representing a persisted session record."""
+
+    model_config = ConfigDict(strict=True)
+
+    id: int = Field(..., description="Auto-incremented row ID.")
+    token: str = Field(..., description="Opaque session token.")
+    created_at: str = Field(..., description="ISO 8601 UTC creation timestamp.")
+    expires_at: str = Field(..., description="ISO 8601 UTC expiry timestamp.")