feat: production build with FastAPI static file serving for SPA

- Add StaticFiles mount for /assets
- Add catch-all route serving index.html for SPA client routing
- Frontend build: 101KB gzipped total

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/mqtt_home/main.py

@@ -1,14 +1,17 @@
 import asyncio
 import logging
 import sys
+import pathlib
 from contextlib import asynccontextmanager
 
 # Windows compatibility: use SelectorEventLoop for paho-mqtt (add_reader/add_writer)
 if sys.platform == "win32":
     asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
 
-from fastapi import FastAPI
+from fastapi import FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
+from fastapi.staticfiles import StaticFiles
+from fastapi.responses import FileResponse
 
 from mqtt_home.config import get_settings
 from mqtt_home.database import init_db, get_session_factory, Base
@@ -87,3 +90,15 @@ async def health():
         "status": "ok",
         "mqtt_connected": mqtt.is_connected if mqtt else False,
     }
+
+# Serve frontend static files in production
+_frontend_dist = pathlib.Path(__file__).parent.parent.parent / "frontend" / "dist"
+if _frontend_dist.exists():
+    app.mount("/assets", StaticFiles(directory=str(_frontend_dist / "assets")), name="assets")
+
+    @app.get("/{full_path:path}")
+    async def serve_spa(full_path: str):
+        file = _frontend_dist / full_path
+        if file.exists() and file.is_file():
+            return FileResponse(str(file))
+        return FileResponse(str(_frontend_dist / "index.html"))