#21339 feat(cmux-next): refresh Apps discover home

Refresh the Apps discover home into a useful catalog surface.

• Adds a clear Apps heading and catalog framing.
• Highlights first-party apps using existing catalog data.
• Adds publisher, verification, category, preview, and installed metadata.
• Improves responsive cards, loading skeletons, empty/disconnected states, and reduced-motion behavior.

Verification:

• bun run typecheck
• bun run lint
• bun test test/gallery-coverage.test.ts
• Chromium and WebKit page flow: discover/search/category/detail/back/install/Installed
• git diff --check

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Summary by cubic

Refreshes the Apps discover home into a catalog surface that highlights first-party apps and surfaces richer metadata.

Previously, discover showed a plain grid of cards with just name, description, and an install button, plus bare disconnected and empty messages with no loading state. Now the page opens with a clear Apps heading, a featured section for the top first-party apps by install count, and a catalog grid. Cards show publisher, verified, category, and preview metadata; publisher names now sit on the page's caption type scale and wrap so long names stay legible. The row layout also gains publisher info. Loading shows skeleton cards instead of blank space, and empty/disconnected states use styled icons and messages. Card styling uses the page's elevation tokens and type-scale variables across headings, captions, and detail text, and hover effects and skeleton animations are disabled under prefers-reduced-motion.

Verification:

• bun run typecheck
• bun run lint
• bun test test/gallery-coverage.test.ts
• Chromium and WebKit page flow: discover/search/category/detail/back/install/Installed
• git diff --check