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/qml/controls/QbzLineEdit.qml

@@ -224,6 +224,7 @@ Rectangle {
                 // No clip: TextInput scissors itself (:207) and the
                 // placeholder elides. A redundant second scissor.
                 TextInput {
+                    QbzTextEditMenu { }
                     id: input
                     anchors.fill: parent
                     color: theme.textPrimary