fix: serve frontend in production — multi-stage Dockerfile with Node build + StaticFiles mount

- Dockerfile: add Node.js frontend build stage (vite build)
- Dockerfile: copy frontend/dist into runtime image
- app/main.py: mount /assets static files + SPA catch-all fallback
- app/main.py: serve index.html for all non-API routes
- Fixes: https://crm.media-on.de/ returning 404 (frontend not served)

app/main.py

@@ -6,9 +6,12 @@ import time
 import traceback
 from contextlib import asynccontextmanager
 
-from fastapi import FastAPI, Request
+from fastapi import FastAPI, HTTPException, Request
 from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import FileResponse
+from fastapi.staticfiles import StaticFiles
 from starlette.middleware.base import BaseHTTPMiddleware
+import os
 
 from app.config import get_settings
 from app.core.db import close_engine, get_engine
@@ -123,6 +126,27 @@ def create_app() -> FastAPI:
     app.include_router(ai_copilot.router)
     app.include_router(workflows.router)
 
+    # ─── Serve frontend static files (SPA) ───────────────────────────────
+    # Mount built frontend assets (JS, CSS, images)
+    frontend_dist = os.path.join(os.path.dirname(__file__), "..", "frontend", "dist")
+    if os.path.isdir(frontend_dist):
+        # Serve static assets at /assets
+        assets_path = os.path.join(frontend_dist, "assets")
+        if os.path.isdir(assets_path):
+            app.mount("/assets", StaticFiles(directory=assets_path), name="assets")
+
+        # SPA catch-all: serve index.html for all non-API routes
+        @app.get("/{full_path:path}")
+        async def spa_spa(full_path: str):
+            """Serve index.html for all non-API routes (SPA fallback)."""
+            # Don't intercept API routes
+            if full_path.startswith(("api/", "docs", "openapi", "redoc")):
+                raise HTTPException(status_code=404, detail="Not Found")
+            index_path = os.path.join(frontend_dist, "index.html")
+            if os.path.isfile(index_path):
+                return FileResponse(index_path)
+            raise HTTPException(status_code=404, detail="Frontend not built")
+
     return app