Fix duplicate theme insertion when API returns multiple versions

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

backend/app/openings_downloader/services/animethemes.py

@@ -205,11 +205,13 @@ class AnimeThemesService:
 
             key = (theme_type, sequence)
             if key in existing_themes:
-                # Update existing theme
+                # Update existing theme (skip if already has video_url)
                 theme = existing_themes[key]
-                theme.song_title = song_title
-                theme.artist = artist
-                if video_url:
+                if not theme.song_title:
+                    theme.song_title = song_title
+                if not theme.artist:
+                    theme.artist = artist
+                if video_url and not theme.animethemes_video_url:
                     theme.animethemes_video_url = video_url
             else:
                 # Create new theme
@@ -225,6 +227,8 @@ class AnimeThemesService:
                 if anime.themes is None:
                     anime.themes = []
                 anime.themes.append(theme)
+                # Add to existing_themes to avoid duplicates from API
+                existing_themes[key] = theme
 
         await db.commit()