v0.55.0: Kaleidostrobe smooth again; visualizer tile hover controls

The cones move only on the plugin's own 25 fps frames again: driving them
from fresh audio every refresh made bass-heavy songs twitch (a jump on 84%
of refreshes against 41%). The continuous turn, texture crossfade and the
GPU big window stay.

The tile: a click opens it big (and it stays blank while big); hovering
shows a colour wheel (colour / gray / off) and up/down arrows (previous /
next visualizer). No more double-click or click-to-cycle. The big album
art closes on a click or Esc, like the big visualizer.

tests/test_round18.py

@@ -68,7 +68,7 @@ class TestVisualizerModePersistence:
         prefs = Preferences(tmp_path)
         vis = VisualizerWidget(_FakePlayer(), prefs)
 
-        vis.mousePressEvent(None)  # on -> dim
+        vis.cycle_mode()  # on -> dim
 
         assert prefs.get("visualizer_mode") == MODE_DIM
         # A fresh Preferences (= next launch) sees it too.