fix(qt): ambient mode reaches every chrome control

Under the ambient field some controls still painted the opaque theme
token while their neighbours used the half-alpha one: the album track
filter and its select toggle, the Library tab strip's host, the Local
Library icon selects, the header's active nav items and open playlists
button, the queue sidebar's now-playing card and artwork placeholders,
the Listen list's floating actions, and the shared SettingsButton,
IconTextButton, multi-select bar, text area, load-more pill, tree row
selection, sidebar count chips, Purchases tab strip, play-history filter
box and Orbit banner. Each now takes the ambient-aware fill the header
search and QbzTabBar already use (theme.ambientOn ? …A50 : …).

Tooltips, popups and modals stay opaque on purpose: they are read over
content, not chrome.

cc

crates/qbz-qt/qml/controls/IconTextButton.qml

@@ -36,7 +36,7 @@ Rectangle {
     radius: theme.radiusSm
     border.width: 1
     border.color: theme.borderSubtle
-    color: hoverArea.containsMouse && root.btnEnabled ? theme.surfaceHover : theme.surfaceElevated
+    color: hoverArea.containsMouse && root.btnEnabled ? theme.surfaceHover : (theme.ambientOn ? theme.surfaceElevatedA50 : theme.surfaceElevated)
     opacity: root.btnEnabled ? 1.0 : 0.4
 
     Row {