feat(artist): resolve patreon + subscribestar display names at add-time (#130 step 5)

Parity with pixiv (operator ask): the extension add now resolves the real
display name for our other native platforms too, not just the URL handle.
patreon_resolver.resolve_display_name reads the campaigns API's
attributes.name; SubscribeStarClient.resolve_display_name pulls the creator
name off the profile page (og:title, else the <title> stripped of the
SubscribeStar suffix). extension_service._resolve_artist_name dispatches per
platform (pixiv=token, patreon/subscribestar=cookies via get_cookies_path),
best-effort in an executor, falling back to the readable URL handle on any
failure. Still all curator core — the extension is unchanged (sends only the
URL). gallery-dl platforms keep the handle (readable, no native client).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

tests/test_patreon_resolver.py

@@ -5,9 +5,34 @@ import pytest
 from backend.app.services.patreon_resolver import (
     resolve_campaign_id,
     resolve_campaign_id_for_source,
+    resolve_display_name,
 )
 
 
+def test_resolve_display_name_from_campaign():
+    fake = MagicMock()
+    fake.status_code = 200
+    fake.json.return_value = {"data": [
+        {"id": "1", "type": "campaign", "attributes": {"name": "Maewix Studios"}},
+    ]}
+    with patch("backend.app.services.patreon_resolver.requests.get", return_value=fake):
+        assert resolve_display_name("maewix", None) == "Maewix Studios"
+
+
+def test_resolve_display_name_none_on_empty_or_error():
+    empty = MagicMock()
+    empty.status_code = 200
+    empty.json.return_value = {"data": []}
+    with patch("backend.app.services.patreon_resolver.requests.get", return_value=empty):
+        assert resolve_display_name("maewix", None) is None
+    import requests as _rq
+    with patch(
+        "backend.app.services.patreon_resolver.requests.get",
+        side_effect=_rq.ConnectionError("x"),
+    ):
+        assert resolve_display_name("maewix", None) is None
+
+
 @pytest.mark.asyncio
 async def test_resolves_on_happy_path():
     fake_response = MagicMock()