fix: OG scrape fills missing artist even when JSON-LD found track name

JSON-LD could set track_name but return empty byArtist, making the OG
block (guarded by `if not track_name`) never run — leaving artist blank.
Now OG runs whenever either name or artist is missing, and only fills
fields that are still empty so JSON-LD name isn't overwritten.

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

backend/spotify_resolve.py

@@ -111,19 +111,21 @@ def resolve(sp_type, sp_id):
                     except Exception as e:
                         eprint(f'[spotapi] JSON-LD parse failed: {e}')
 
-                # 2) OG tags — artist is desc_parts[0], then type ("Song"), then year
-                if not track_name:
+                # 2) OG tags — fill in any fields still missing after JSON-LD
+                # Real format: "Artist · Song · Year" — artist is index 0
+                if not track_name or not artist_name:
                     og = {}
                     for m in re.finditer(r'<meta\s+(?:property|name)=["\']og:([^"\']+)["\']\s+content=["\']([^"\']*)["\']', page):
                         og[m.group(1)] = _html.unescape(m.group(2))
                     for m in re.finditer(r'<meta\s+content=["\']([^"\']*)["\'][^>]+(?:property|name)=["\']og:([^"\']+)["\']', page):
                         og[m.group(2)] = _html.unescape(m.group(1))
                     desc_parts = [p.strip() for p in og.get('description', '').split('·')]
-                    track_name  = og.get('title', '')
-                    # Real format: "Artist · Song · Year · N songs." — artist is index 0
-                    artist_name = desc_parts[0] if desc_parts else ''
-                    album_name  = ''
-                    art_url     = og.get('image', '')
+                    if not track_name:
+                        track_name = og.get('title', '')
+                    if not artist_name:
+                        artist_name = desc_parts[0] if desc_parts else ''
+                    if not art_url:
+                        art_url = og.get('image', '')
                     eprint(f'[spotapi] OG scrape: name={track_name!r} artist={artist_name!r}')
 
                 if track_name: