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

backend/app/services/patreon_resolver.py

@@ -139,6 +139,32 @@ def _lookup_via_api(vanity: str, cookies_path: str | None) -> str | None:
     return campaign_id
 
 
+def resolve_display_name(vanity: str, cookies_path: str | None) -> str | None:
+    """The Patreon campaign's display name for `vanity` via the campaigns API
+    (`fields[campaign]=name`), used to name the Artist at add-time (#130). None
+    on any failure — the caller falls back to the vanity handle. Sync: call from
+    an executor."""
+    jar = _load_cookie_jar(cookies_path)
+    try:
+        resp = requests.get(
+            _CAMPAIGNS_URL,
+            params={"filter[vanity]": vanity, "fields[campaign]": "name"},
+            headers={"User-Agent": _USER_AGENT, "Accept": "application/vnd.api+json"},
+            cookies=jar,
+            timeout=_TIMEOUT_SECONDS,
+        )
+        if resp.status_code != 200:
+            return None
+        data = resp.json().get("data")
+    except (requests.RequestException, ValueError) as exc:
+        log.warning("Patreon name lookup failed for vanity=%s: %s", vanity, exc)
+        return None
+    if not isinstance(data, list) or not data or not isinstance(data[0], dict):
+        return None
+    name = (data[0].get("attributes") or {}).get("name")
+    return name.strip() if isinstance(name, str) and name.strip() else None
+
+
 def _scrape_campaign_id(html: str) -> str | None:
     """First campaign id found in creator-page HTML via the known embeddings."""
     if not isinstance(html, str):