feat(ui): polish workspace states

[flamboh]

Summary

• reuse one multi-format audio import surface on the landing page and in the empty editor
• keep media URL state across layout changes while unmounting the entry from Settings
• add accessible album validation and cover-processing semantics
• make saved feedback transient and announce it to assistive technology
• prevent accidental checkbox-label text selection

Why

This rebuild preserves the useful product behavior from #120 without carrying forward its obsolete MP3-only assumptions or pre-sharing workspace structure. Empty states become useful import surfaces, and forms provide honest, bounded feedback.

Replacement

Replaces #120. The old PR should remain open until this replacement and the combined advanced-metadata replacement are traceable.

This draft is intentionally based on current main. The advanced-metadata replacement is planned to merge first; this branch will be rebased afterward because both changes touch the editor shell.

Verification

• bun run typecheck
• bun run lint — 0 warnings/errors
• bun run test — 90 files, 554 tests passed
• bun run build
• git diff --check

The updated Playwright coverage was authored but not executed because no server was already available, and project instructions prohibit starting one for this workflow.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	tagium	b5c1314	Commit Preview URL Branch Preview URL	Jul 25 2026, 08:30 AM

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit b5c1314.}