#21442 Gallery: make current-composer handoff fast and shareable

Summary

Add a usable, exact-head gallery handoff for the current composer fixture.

Changelog

• Added permalink, copy-link, and Team feed actions to the gallery shell.
• Resolve direct gallery routes as soon as the named lazy entry loads.
• Keep gallery chrome aligned with the selected app theme.
• Record the verified live feed route and managed preview receipt.

Proof

• Live gallery: https://cmux-lawrences-mac-mini.tail137216.ts.net:18796/wt/leo-current-composer-visual-20261017/?entry=agent-pane.new-tab&variant=current-composer#/agent-pane.new-tab/current-composer
• Team feed: https://cmux-lawrences-mac-mini.tail137216.ts.net:8443/feed/
• Managed build tip: 1d0d1132e68dc673188dd150b16df547f1733386
• Gallery typecheck: bun run typecheck passed (1477 files)

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Summary by cubic

Makes gallery handoff of the current-composer fixture faster and shareable: permalinks, copy-link, and Team feed actions are now in the shell, and named deep-link routes resolve as soon as that entry loads instead of waiting for the whole registry.

• Adds the current-composer visual-only variant for the New Tab surface, with seeded quiet chat rows and a check that no Release journey rows appear.
• Adds waitFor(id) to the entry store so deep links render immediately; remaining entries still load in the background.
• Makes the gallery chrome follow the selected app theme, and labels every preview as either a component surface or a window-pane view with rendered dimensions.
• Shows each fixture's purpose note on browse cards.
• Records the fixture mandate, acceptance criteria, and managed receipt hashes in plans/cmux-next/evidence/current-composer-visual-20261017.md.