Library art: real gameplay instead of GitHub social cards; accept GIF sources

GitHub's opengraph preview is repo text, stats and an identicon; as a Steam hero
it looked broken. GitHub entries no longer default to it (the store draws its
fallback, Steam gets generated art). Source GIFs (common gameplay captures) are
accepted; the Frame's Chromium draws the first frame. Open Saber Plus uses its
gameplay GIF as banner. Verified on the Frame: hero/wide now show gameplay.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

ui/apk_sources/github.py

@@ -35,7 +35,8 @@ def _entry(source, c, approved=True):
     artwork = c.get('images') or {}
     icon = artwork.get('icon') or c.get('icon') or 'https://github.com/' + c['repo'].split('/')[0] + '.png'
     images = {'icon': icon,
-              'banner': artwork.get('banner') or 'https://opengraph.githubassets.com/1/' + c['repo'],
+              # No GitHub social-preview card: it's repo text and stats, not art; the UI draws a fallback.
+              'banner': artwork.get('banner'),
               'screenshots': list(artwork.get('screenshots') or [])}
     return {'source': source['id'], 'id': c['repo'], 'package': None,
             'name': c['name'], 'summary': c.get('summary') or '', 'icon': icon,