feat(slint): new now-playing bar layout

Land the "New" now-playing bar as the first of the four switchable
layouts. A dedicated SongCard component holds the cover (or an idle
sleeping cat), the elidable title, the artist·album links, and the
vertical audio stamp (compact quality badge over the backend/mode LEDs).
A full-width seek bar sits on top with a buffer-driven stream lock.

The controls row uses responsive symmetric column zones (39/30/25% by
window width); the side columns share one fraction so the transport stays
absolutely centred and PLAY lands on the window centre. The song-card /
controls divider is a hard wall: the text column stretches to push the
audio stamp to its right edge, the album elides first (and never collapses
to zero) so the stamp is always visible and never crosses the wall.

Adds QualityBadgeFull compact mode, backend/mode output LED labels from
settings, a global TooltipOverlay so clipped columns keep their tooltips,
and the supporting icons.

cc

crates/qbz-slint/ui/state.slint

@@ -1311,6 +1311,19 @@ export global SettingsState {
     in-out property <bool> gapless: true;
     in-out property <bool> stream-uncached: false;
     in-out property <bool> streaming-only: false;
+    // Volume normalization (loudness leveling). Applied in the shared player
+    // and bypassed automatically when bit-perfect is active. Surfaced in the
+    // now-playing bar's normalization group as well as Settings > Playback.
+    in-out property <bool> normalization: false;
+
+    // Audio-output indicators for the now-playing song card (computed in Rust
+    // from the real backend + bit-perfect constraints). `*-label` is the fixed
+    // short text; `*-active` colours the led when a deliberate / bit-perfect
+    // mode is engaged (vs the shared system default).
+    in-out property <string> output-backend-label: "SYST";   // PIPE|ALSA|JACK|PULS|SYST
+    in-out property <string> output-mode-label: "DEFAULT";    // DACPASS|BITPERF|EXCL|DIRECT|LOCKED|ROUTED|SHARED|DEFAULT
+    in-out property <bool> output-backend-active: false;
+    in-out property <bool> output-mode-active: false;
 
     // Playback — Initial Buffer Size slider (seconds, 1-10).
     in-out property <int> buffer-seconds: 3;
@@ -1904,6 +1917,10 @@ export global NowPlayingState {
     in property <int> duration-secs: 0;
     in property <float> progress: 0.0;   // 0..1
     in property <float> cache: 0.0;       // 0..1 buffered
+    // Furthest seekable fraction. 1.0 for fully-available (local/cached)
+    // tracks; equal to the streamed buffer while a track is still downloading,
+    // so the user can't seek into not-yet-downloaded territory.
+    in property <float> seekable-max: 1.0;
     in property <string> elapsed: "0:00";
     in property <string> remaining: "0:00";
     in property <float> volume: 0.7;      // 0..1
@@ -1911,6 +1928,32 @@ export global NowPlayingState {
     in property <bool> shuffle: false;
     in property <int> repeat-mode: 0;     // 0 off, 1 all, 2 one
 
+    // Quality of the playing track, for the song-card badge.
+    in property <string> quality-tier;    // "hires" | "cd" | "mp3" | ""
+    in property <string> quality-detail;  // "24-bit / 96 kHz"
+
+    // Cast / render-aware state (Qobuz Connect). `is-remote` = a peer
+    // renderer owns playback (controls route to it); `volume-locked` =
+    // the active renderer disallows remote volume control. Both default
+    // off and are wired by the QConnect epic; the bar respects them now.
+    in property <bool> is-remote: false;
+    in property <bool> volume-locked: false;
+    // Name of the active Qobuz Connect renderer (shown under the cast button
+    // when remote). Empty when local. Populated by the QConnect epic.
+    in property <string> cast-target;
+
+    // Cast (Chromecast / DLNA) — when casting, the two output leds fuse into a
+    // single purple CAST / DLNA led (mirroring Tauri). Populated by the Cast epic.
+    in property <bool> cast-active: false;
+    in property <string> cast-protocol;  // "cast" | "dlna"
+
+    // Playback CONTEXT — the source the queue was launched from (album /
+    // playlist / artist / label / mix). Drives the song-card layers button
+    // (navigate back to that page). Set at play time, persists across track
+    // changes; falls back to the track's album when no richer source is known.
+    in property <string> context-kind;  // "album" | "playlist" | "artist" | "label" | "mix"
+    in property <string> context-id;
+
     // Transport callbacks, wired to the Rust playback controller.
     callback toggle-play();
     callback next();
@@ -1922,6 +1965,17 @@ export global NowPlayingState {
     callback cycle-repeat();
 }
 
+// Single global hover-tooltip channel. Each hoverable control writes its text
+// + absolute anchor (window coords: centre-x and top-y of the control) here on
+// hover; one TooltipOverlay (mounted last, on top of everything) renders the
+// bubble, clamped to the window so it never clips or hides behind a neighbour.
+export global TooltipState {
+    in-out property <string> text;
+    in-out property <length> anchor-x;  // control centre, window coords
+    in-out property <length> anchor-y;  // control top, window coords
+    in-out property <bool> show: false;
+}
+
 // Playback queue model, for the Queue sidebar.
 //
 // The sidebar shows two tabs. The Queue tab renders `now-playing` plus a