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/tests/test_routers/test_health.py

@@ -0,0 +1,26 @@
+"""Tests for the health check router."""
+
+import pytest
+from httpx import AsyncClient
+
+
+@pytest.mark.asyncio
+async def test_health_check_returns_200(client: AsyncClient) -> None:
+    """``GET /api/health`` must return HTTP 200."""
+    response = await client.get("/api/health")
+    assert response.status_code == 200
+
+
+@pytest.mark.asyncio
+async def test_health_check_returns_ok_status(client: AsyncClient) -> None:
+    """``GET /api/health`` must return ``{"status": "ok"}``."""
+    response = await client.get("/api/health")
+    data: dict[str, str] = response.json()
+    assert data == {"status": "ok"}
+
+
+@pytest.mark.asyncio
+async def test_health_check_content_type_is_json(client: AsyncClient) -> None:
+    """``GET /api/health`` must set the ``Content-Type`` header to JSON."""
+    response = await client.get("/api/health")
+    assert "application/json" in response.headers.get("content-type", "")