feat(qt): overAmbient legibility mode for the quality badge and track info

Immersive surfaces sit directly on the ambient field, where theme tokens
have no contrast guarantee — a light cover washed the split Track Info
panel and the quality badges out completely. QualityBadgeFull,
TrackInfoBody, InfoMetaCell and InfoCreditCell gain an opt-in overAmbient
mode: fixed light text with the restrained native shadow the lyrics
surfaces already use, and the badge swaps the theme surface for its own
translucent dark scrim covering only the chip. Defaults stay off, so the
desktop modal and every themed mount are untouched. The immersive Track
Info panel and song card opt in.

cc

crates/qbz-qt/qml/immersive/TrackInfoPanel.qml

@@ -105,6 +105,8 @@ Item {
             anchors.centerIn: parent
             text: QbzSession.tr("No track selected", QbzSession.trRev)
             color: "#b3ffffff"
+            style: Text.Raised
+            styleColor: "#b0000000"
             font.pixelSize: 18
         }
 
@@ -123,6 +125,9 @@ Item {
                 id: body
                 host: host
                 width: flick.width
+                // The panel sits on the ambient field — fixed light colors
+                // + native shadow (2026-08-31 visual cleanup).
+                overAmbient: true
             }
         }