feat(proxy): add service CRUD with persistent storage

ServiceManager with JSON file persistence replaces static env var config.
CRUD API endpoints (POST/PUT/DELETE /api/services) with WebSocket broadcast.
Dashboard: add/edit/delete services via modal form.

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

compose.yaml

@@ -7,6 +7,8 @@ services:
       - "47391:47391"
     env_file:
       - .env
+    volumes:
+      - ./data/proxy:/app/data
     restart: unless-stopped
 
   agent: