Add FastAPI backend and React frontend subprojects

Backend:
- FastAPI app with 17 REST endpoints covering dashboard, monitoring,
  media index, file browser, and jobs
- Reuses existing clients/domain/services unchanged
- pydantic-settings config, dependency injection, CORS setup
- Auto-generated OpenAPI docs at /docs

Frontend:
- Vite + React + TypeScript SPA
- @tanstack/react-query for data fetching with polling
- ag-grid-react for media table and file browser
- recharts for monitoring charts
- Tailwind CSS styling
- 4 pages: Dashboard, Monitoring, Media, File Browser
- Typed API client matching all backend endpoints

Also:
- docs/MIGRATION_PLAN.md with full architecture plan
- Updated .gitignore for both subprojects
- Streamlit app preserved for now (can coexist)

frontend/src/components/LibraryOverview.tsx

@@ -0,0 +1,55 @@
+import type { LibraryCount } from "../types";
+
+interface Props {
+	libraries: LibraryCount[];
+}
+
+export function LibraryOverview({ libraries }: Props) {
+	const movieLibs = libraries.filter((l) => l.type === "movies");
+	const tvLibs = libraries.filter((l) => l.type === "tvshows");
+
+	return (
+		<div className="grid grid-cols-2 gap-6">
+			{movieLibs.length > 0 && (
+				<div>
+					<p className="text-xs text-gray-500 uppercase tracking-wide mb-2">
+						Movie libraries
+					</p>
+					{movieLibs.map((lib) => (
+						<div key={lib.library} className="rounded-lg border p-4 mb-2">
+							<p className="font-semibold">{lib.library}</p>
+							<div className="flex gap-6 mt-2 text-sm">
+								<span>
+									Total: <strong>{lib.total.toLocaleString()}</strong>
+								</span>
+								<span>
+									Movies: <strong>{lib.movies.toLocaleString()}</strong>
+								</span>
+							</div>
+						</div>
+					))}
+				</div>
+			)}
+			{tvLibs.length > 0 && (
+				<div>
+					<p className="text-xs text-gray-500 uppercase tracking-wide mb-2">
+						TV libraries
+					</p>
+					{tvLibs.map((lib) => (
+						<div key={lib.library} className="rounded-lg border p-4 mb-2">
+							<p className="font-semibold">{lib.library}</p>
+							<div className="flex gap-6 mt-2 text-sm">
+								<span>
+									Total: <strong>{lib.total.toLocaleString()}</strong>
+								</span>
+								<span>
+									Series: <strong>{lib.series.toLocaleString()}</strong>
+								</span>
+							</div>
+						</div>
+					))}
+				</div>
+			)}
+		</div>
+	);
+}