fix(locallibrary): track-row source indicator (drop fav/offline) + AlbumView favorite item

LocalLibrary track rows (Tracks tab + local album detail) no longer carry the
favorite or offline-cache columns — they don't apply to local content. Instead
they show a subtle per-source indicator (local -> hard-drive tinted; qobuz
offline / plex -> their mark), small + flat rather than the bold album-card
badge (mirrors Tauri's track-row local indicator). TrackItem gains a `source`
field, set by every constructor (Qobuz surfaces -> "qobuz"; map_local_track ->
local/qobuz/plex); TrackRow gains `show-source`.

Also fixes Qobuz AlbumView: the track list had a Favorite column header but the
rows never rendered the heart (show-favorite defaulted false). AlbumPageView
now sets show-favorite + show-download for Qobuz albums (matching the header)
and the source indicator for local albums, with the column header switched to
match each.

cc

crates/qbz-slint/ui/state.slint

@@ -251,6 +251,9 @@ export struct TrackItem {
     // album view, both via the media-action bubble channel.
     artist-id: string,
     album-id: string,
+    // "qobuz" | "local" | "plex" | "" — drives the Local Library source
+    // indicator (shown instead of the favorite/offline columns).
+    source: string,
     // Fading out (un-favorited in the favorites view) before removal.
     removing: bool,
     // Offline-cache status: 0 none, 1 queued, 2 downloading, 3 ready, 4 failed.