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

frontend/src/App.tsx

@@ -0,0 +1,45 @@
+/**
+ * Application root component.
+ *
+ * Wraps the entire application in:
+ *  1. `FluentProvider` — supplies the Fluent UI theme and design tokens.
+ *  2. `BrowserRouter` — enables client-side routing via React Router.
+ *
+ * Route definitions are delegated to `AppRoutes` (implemented in Stage 3).
+ * For now a placeholder component is rendered so the app can start and the
+ * theme can be verified.
+ */
+
+import { FluentProvider } from "@fluentui/react-components";
+import { BrowserRouter } from "react-router-dom";
+import { lightTheme } from "./theme/customTheme";
+
+/**
+ * Temporary placeholder shown until full routing is wired up in Stage 3.
+ */
+function AppPlaceholder(): JSX.Element {
+  return (
+    <div style={{ padding: 32, fontFamily: "Segoe UI, sans-serif" }}>
+      <h1 style={{ fontSize: 28, fontWeight: 600 }}>BanGUI</h1>
+      <p style={{ fontSize: 14, color: "#605e5c" }}>
+        Frontend scaffolding complete. Full UI implemented in Stage 3.
+      </p>
+    </div>
+  );
+}
+
+/**
+ * Root application component.
+ * Mounts `FluentProvider` and `BrowserRouter` around all page content.
+ */
+function App(): JSX.Element {
+  return (
+    <FluentProvider theme={lightTheme}>
+      <BrowserRouter>
+        <AppPlaceholder />
+      </BrowserRouter>
+    </FluentProvider>
+  );
+}
+
+export default App;