feat(qbz-qt): phase 7 — shared AlbumCard, rounded frameless window, sidebar playlist tree

One AlbumCard.qml replicating the Slint shared card (pin badge with
PinnedItemsService wired, heart, hover play overlay, exact context
menu with Play next/Add to queue wired) used by BOTH Home rails and
the Library All grid. Frameless translucent window with 12px rounded
corners, replicated WindowControls, header drag, 8 resize grips.
Sidebar playlist tree: 56 playlists / 12 folders live, expand state,
5-option sort with direction caret, recursive search filter, collage
covers, create-playlist wired. Fixed a std-Mutex self-deadlock in the
sidebar loader (two lock temporaries in one log statement).

km

crates/qbz-qt/build.rs

@@ -40,6 +40,7 @@ fn main() {
                 "qml/Main.qml",
                 "qml/LoginScreen.qml",
                 "qml/AppShell.qml",
+                "qml/AlbumCard.qml",
                 "qml/Sidebar.qml",
                 "qml/HeaderBar.qml",
                 "qml/NowPlayingBarSmall.qml",