Messages: cross-post URL labels, viewerHasMuted, and scheduled cross-post config #38

Three live response fields the app drops on the floor.

crossPostUrls

The web feed shows per-platform labels under a post ("Mastodon (metalhead.club)", "Bluesky", "linkedin") linking to the syndicated copy — visible on the public landing page. The app shows nothing.

• Model CrossPostUrls and render one label per platform, opening the target in the OS browser.

viewerHasMuted

Each message reports whether the viewer has muted its author.

• Model ViewerHasMuted and collapse/soften such cards instead of rendering them identically to the rest.

scheduledCrossPostConfig

A scheduled post carries the cross-post selection it will use when it fires.

• Model it and show, in the scheduled-posts view, which platforms a pending post will syndicate to.