feat(qbz-qt): phase 4 — live playback, queue, and transport via QbzCore

Album-card click plays the album: get_album -> QueueTrack vec ->
set_queue -> play_track_resolved (tier walk stays in the core). 1 Hz
poll publishes position/meta/quality into the NowPlaying model; end-of-
track edge auto-advances with meta refresh (traced live: 24-bit/48kHz
CMAF stream, position advancing, track 2/3 transitions). Transport
invokables rewired to real core calls; queue panel shows NOW PLAYING +
numbered UP NEXT from get_queue_state. Public QbzCore API proved
sufficient — protected audio/player crates untouched. Named gaps:
no mute API, no playback event stream, auto-advance/prefetch semantics
remain frontend glue (~150 lines every UI must port).

km

crates/qbz-qt/qml/HomeView.qml

@@ -162,7 +162,9 @@ Rectangle {
                     anchors.fill: parent
                     hoverEnabled: true
                     cursorShape: Qt.PointingHandCursor
-                    // POC-NOTE: the album page is out of scope — inert.
+                    // Phase 4: a card click plays the album (the album page
+                    // itself is out of scope — POC-NOTE).
+                    onClicked: QbzBridge.playAlbum(card.id)
                 }
                 // Hover action buttons — favorite / play / more (INERT;
                 // POC-NOTE: playback + favorites land in later phases).
@@ -208,7 +210,13 @@ Rectangle {
                             anchors.centerIn: parent
                             tintName: "black"
                         }
-                        MouseArea { id: playOvArea; anchors.fill: parent; hoverEnabled: true; cursorShape: Qt.PointingHandCursor }
+                        MouseArea {
+                            id: playOvArea
+                            anchors.fill: parent
+                            hoverEnabled: true
+                            cursorShape: Qt.PointingHandCursor
+                            onClicked: QbzBridge.playAlbum(card.id)
+                        }
                     }
                     Rectangle {
                         width: 36
@@ -437,7 +445,8 @@ Rectangle {
             anchors.fill: parent
             hoverEnabled: true
             cursorShape: Qt.PointingHandCursor
-            // POC-NOTE: album page out of scope — inert.
+            // Phase 4: slim rows are albums — click plays (page out of scope).
+            onClicked: QbzBridge.playAlbum(card.id)
         }
     }