Social platform icon sources

These icons are bundled in the asset catalog and used for account identity throughout the app.

• Bluesky butterfly: official Bluesky brand assets, blue transparent PNG.
• Mastodon mark: official Mastodon brand toolkit, purple SVG mark.
• GitHub mark: Simple Icons CDN, white GitHub mark on its black circular background. GitHub is available as a manual social account; it is not an API-connected SocialKit provider.

The existing Facebook, Instagram, LinkedIn, Threads, and X assets remain as they were.