feat(qt): say "not yet available" on pre-release tracks

/album/get sends streamable_at and release_date_stream per track: a future
value marks a pre-release, null a pulled track. Track carries both fields
and Track::is_upcoming applies the one rule (future streamable_at wins,
then a future release date); the album, playlist, search and label rows
publish qobuzUpcoming and the unavailable glyph reads "This track is not
yet available" instead of "no longer". Artist page rows carry no dates and
keep the generic copy. New msgid in the seven translated catalogs.

cc

crates/qbz-qt/qml/views/ArtistView.qml

@@ -1158,10 +1158,12 @@ Rectangle {
                             hoverEnabled: true
                             ToolTip.visible: containsMouse
                             ToolTip.delay: 300
-                            // REUSED msgid (es:3658) — the same sentence the
-                            // reactive skip path toasts.
-                            ToolTip.text: QbzSession.tr(
-                                "This track is no longer available", QbzSession.trRev)
+                            // Same split as rows/TrackRow.qml: a pre-release
+                            // says "not yet", a pulled track keeps the REUSED
+                            // msgid the reactive skip path toasts.
+                            ToolTip.text: row.qobuzUpcoming === true
+                                ? QbzSession.tr("This track is not yet available", QbzSession.trRev)
+                                : QbzSession.tr("This track is no longer available", QbzSession.trRev)
                         }
                     }
                 }