Fix Docker configuration for new backend structure

- Update Dockerfile to use backend.main:app instead of main:app
- Change exposed port from 8000 to 8001
- Fix docker-compose.yml port mapping to 8001:8001
- Update healthcheck to use correct port and /health endpoint
- Remove old main.py from root directory

Docker now correctly runs the new frontend + backend structure.

docker-compose.yml

@@ -5,15 +5,15 @@ services:
     build: .
     container_name: seismo-fleet-manager
     ports:
-      - "8001:8000"
+      - "8001:8001"
     volumes:
-      # Persist SQLite database
+      # Persist SQLite database and photos
       - ./data:/app/data
     environment:
       - PYTHONUNBUFFERED=1
     restart: unless-stopped
     healthcheck:
-      test: ["CMD", "curl", "-f", "http://localhost:8000/"]
+      test: ["CMD", "curl", "-f", "http://localhost:8001/health"]
       interval: 30s
       timeout: 10s
       retries: 3