Preserve Library view state across sources and playlists

[rianjs]

Library view state

Status: approved; phase 1 in progress on feature/library-view-state.

Approved outcomes

1. Playlist views provide a Back to current Library source action.
2. Music, Podcasts, and Audiobooks preserve their own selected facet drill-down while switching sources and playlists.
3. Playlist column visibility, order, and widths are independent per playlist, with no persisted override for defaults.
4. Library default visible order: Track #, Song, Artist, Album, Time, Plays, Rating, Genre.
5. Playlist default visible order: fixed Spotify order #, Song, Artist, Album, Time, Rating, Plays, Genre.
6. Remove genre override dots.
7. Music Uncategorized renders muted as No Genre; non-Music Uncategorized remains literal.
8. UI navigation never replaces the playback queue; explicit play alone establishes it.
9. Five separate commits, UI first, playback last.
10. Update persistence/playback architecture docs where their contracts change.
11. Add the smallest regression tests and run exact relevant checks.
12. Later delivery uses one Terra-high TDD assessment and capped cr review loop; do not run those now.

Acceptance criteria

• A playlist view has a full-width Back to Music, Back to Podcasts, or Back to Audiobooks action using the existing Spotify page-back visual language, and it returns to the current source's Library view.
• Each source remembers its own category, artist, and album facet selections for the session. Changing source restores that source's selection; entering and leaving a playlist does not clear the active source selection.
• A stale remembered facet follows the existing hierarchical fallback behavior and clears only the invalid level required by the resolved browse projection.
• Search query and scroll position are not persisted as part of the view state.
• Playlist column visibility, order, and widths are independent for each playlist and defaults have no persisted override.
• Library and playlist columns match the approved default orders, including the playlist's fixed Spotify order column.
• Genre override markers are absent; Music's Uncategorized displays as muted No Genre, while other sources retain literal Uncategorized.
• Navigating sources, facets, playlists, and Spotify views does not replace the playback queue; only explicit play establishes it.
• The delivery is split into five commits in this order: per-source Library navigation; per-playlist column layouts; genre marker removal; missing music genre display; playback queue independence.
• Persistence and playback architecture documentation is updated in the same commit as any changed persistence or playback contract.
• Focused regression tests cover non-trivial behavior, and the relevant frontend checks pass.

Commit sequence

1. Preserve per-source Library navigation.
2. Give playlists independent column layouts.
3. Remove genre override markers.
4. Display missing music genres consistently.
5. Keep playback queues independent of navigation.

Phase 1 scope

• Create the tracking issue with this complete approved outcome and acceptance-criteria set.
• Create and switch to feature/library-view-state from the current HEAD.
• Implement only commit 1 without committing, pushing, opening a PR, or starting later commits.
• Keep saved facet selections session-only and keyed by Source; update them whenever sel changes.
• Entering a playlist must not clear the active source selection. Selecting a source restores that source's selection.
• Keep the existing stale-facet hierarchical fallback.
• Add the playlist Back to current Library source action.
• Do not persist query or scroll position.
• Add focused tests using the existing frontend test pattern.
• Run only the focused frontend tests and build needed for this slice.
• Do not run the later Terra-high TDD assessment or capped cr review loop.

[rianjs]

Completed by #33 and merged into ui-tweaks.