v0.31.3: header row moves up beside the seek bar; knolled top row

The Library button, the view's header (search box or playlist name) and
the seek row now share one band under the transport boxes, instead of the
seek row hanging alone with a header strip below it. The now-playing panel
caps at 560px and the gaps between controls share the rest evenly; more
room under the menu bar. Long playlist names shrink up to 2pt, then elide.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_round62.py

@@ -23,4 +23,5 @@ def test_every_control_shares_the_now_playing_row(qapp, tmp_path):
 
 def test_seek_row_hangs_under_the_panel(qapp, tmp_path):
     bar = _build_bar(qapp, tmp_path)
-    assert bar._slider.geometry().top() > bar._now_playing.geometry().bottom()
+    slider_top = bar._slider.mapTo(bar, bar._slider.rect().topLeft()).y()
+    assert slider_top > bar._now_playing.geometry().bottom()