fix(patreon): declare aiohttp/yarl deps and use public yarl.URL import

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/tests/services/test_patreon_resolver.py

@@ -1,6 +1,7 @@
 """Unit tests for the Patreon campaign-ID resolver."""
+import asyncio
+
 import aiohttp
-import pytest
 from aioresponses import aioresponses
 
 from app.services.patreon_resolver import resolve_campaign_id
@@ -55,7 +56,6 @@ async def test_network_error_returns_none():
 
 
 async def test_timeout_returns_none():
-    import asyncio
     with aioresponses() as mock:
         mock.get(CAMPAIGNS_URL, exception=asyncio.TimeoutError())
         result = await resolve_campaign_id("mstsu", cookies_path=None)