Add version button opens search dialog to browse recent versions and append to playlist

[jspada200]

Summary

Clicking the "Add version" button should open a search dialog where the user can browse recent versions (backend endpoint may be needed). After a version is selected, it is added to the current playlist in the backend by appending it to the bottom.

Details

There is an "Add version" button in the UI. Currently it does not open a search/browse flow. Desired behavior:

• Frontend: Clicking "Add version" opens a search dialog. The user can browse recent versions (and optionally search). Once a version is selected, the UI calls the backend to add that version to the playlist.
• Backend: Support adding a version to a playlist (append only). If no suitable endpoint exists, add one (e.g. add version to playlist by ID). "Recent versions" may require a new endpoint (e.g. list or search recent versions) for the dialog to use.
• Behavior: The selected version is appended to the bottom of the playlist. Order of existing items is unchanged.

Likely areas: frontend component that renders the Add version button; playlist/version API in core and backend.

Acceptance criteria

• Clicking "Add version" opens a search/browse dialog for versions.
• User can browse recent versions (and search if an endpoint supports it).
• Selecting a version adds that version to the current playlist in the backend (append only).
• New version appears at the bottom of the playlist; existing order is unchanged.
• All changes tested locally
• All relevant automated tests complete successfully
• Verified no existing workflows broken
• For UI changes, screenshots or gif animations of the changes included
• Steps to test included in PR

Out of scope

Changing the order of the playlist (reordering). This issue is append-only; no drag-and-drop or reorder UI.