fix: stabilize playback memory, local library sync and Qt settings

Add shared playback memory profiles, bounded disk-backed playback and storage
selection for desktop and daemon. Preserve gapless during streaming-only playback
and provide explicit cache eviction with playback confirmation.

Stop watcher read events and unchanged scans from rebuilding the local catalog.
Restore playlist/sidebar updates, folder availability feedback and player layout.
Add appearance presets and a radio-based cache settings panel with translated
trade-offs, plus consistent clipboard menus across visible Qt text editors.

Validate with Rust regressions, QML interaction tests, isolated release startup
and idle-library checks; extend the shared local and CI gates.

cx

crates/qbz-qt/build.rs

@@ -580,6 +580,7 @@ fn main() {
                 "qml/controls/QbzEmptyState.qml",
                 "qml/controls/QbzIconButton.qml",
                 "qml/controls/QbzLineEdit.qml",
+                "qml/controls/QbzTextEditMenu.qml",
                 "qml/controls/InputFocusDismiss.qml",
                 "qml/controls/QbzLoadingDots.qml",
                 "qml/controls/QbzLoadMore.qml",
@@ -605,6 +606,7 @@ fn main() {
                 "qml/controls/QbzTooltip.qml",
                 "qml/controls/PanelResizeHandle.qml",
                 "qml/controls/QbzProgressRing.qml",
+                "qml/controls/QbzCompactSeekBar.qml",
                 // Applied-filters tooltip: the trigger a filter control mounts
                 // beside itself (it writes the shell channel QbzTooltip reads).
                 "qml/controls/QbzFilterTip.qml",