Restore the media URL transition and stabilize its empty state

[flamboh]

Summary

Keeps URL importing fully available while refining the media bar across its visible states:

• Removes only the “or import from a url” divider from the populated-library empty-selection screen.
• Keeps the selected-track and empty-selection bars at the same width; the initial landing bar remains compact.
• Restores the shared-element transition so the same URL input glides and resizes between landing, loaded-editor, and empty-editor layouts.
• Preserves reduced-motion behavior and the intentional settings-screen unmount.

Root cause

The transition regression landed in f716382 through PR #135; its parent 412afb3 is the last known-good main commit. That refactor correctly lifted the URL-entry controller so text survived layout changes, but it also split one persistent MediaUrlEntry into mutually exclusive mounts and removed the geometry animation. There was no motion-related product decision in the PR, so this restores the lost behavior while keeping the lifted state.

Human review

1. Start with an empty library. Confirm the compact URL import field and “or import from a url” divider are still present.
2. Add a track. The same URL field should glide to the wider media bar at the bottom of the editor instead of disappearing and reappearing.
3. Clear the track selection. Confirm the URL field remains editable, the divider is absent, and the media bar keeps the same width.
4. Enter text, open Settings, then return. The URL field should restore its text; it is intentionally unmounted while Settings is open.
5. Repeat at mobile and intermediate widths. Check that the bar fits without overlapping the dropzone.
6. With reduced motion enabled, state changes should settle immediately without the shared-element animation.

Review considerations: the landing layout intentionally remains narrower, while both editor states share the wider width. Motion animates real position and width rather than scaling the form, keeping text and controls crisp.

Verification

• bunx vp check
• bun run test — 102 files, 631 tests passed
• bun run build
• bun run test:e2e -- --project=chromium tests/e2e/settings-transition.spec.ts — 10 passed
• Deterministic E2E coverage verifies DOM identity plus intermediate geometry during the landing-to-editor transition
• Unit coverage verifies real position/width keyframes without transform scaling
• Impeccable UI detector — no findings

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	tagium	4ad8a75	Commit Preview URL Branch Preview URL	Aug 03 2026, 07:52 PM

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit 4ad8a75.}