feat: RFCP MVP deployed on VPS

Iteration 1:
- Dark theme with 3-way toggle
- Dynamic heatmap gradient (blue→red)
- Radius up to 100km
- Save & Calculate workflow

Iteration 2:
- Terrain overlay toggle
- Batch height operations
- Zoom-dependent heatmap rendering

Infrastructure:
- Backend FastAPI on 8888
- Frontend static build via Caddy
- Systemd services
- Caddy reverse proxy integration

backend/app/main.py

@@ -0,0 +1,29 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import FileResponse
+import os
+
+app = FastAPI(title="RFCP API")
+
+# CORS
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["https://rfcp.eliah.one", "http://localhost:5173"],
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+@app.get("/health")
+async def health():
+    return {"status": "healthy", "version": "1.0.0"}
+
+@app.get("/api/terrain/{region}")
+async def get_terrain(region: str):
+    terrain_path = f"/opt/rfcp/data/terrain/{region}.hgt"
+    if os.path.exists(terrain_path):
+        return FileResponse(terrain_path)
+    return {"error": "Region not found"}, 404
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run(app, host="0.0.0.0", port=8090)