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_round78.py

@@ -432,11 +432,10 @@ class TestBarsFade:
 # --------------------------------------------------------------------------
 
 class TestBigWindow:
-    def test_double_click_keeps_the_brightness_and_opens(self, qapp, tmp_path):
+    def test_opening_keeps_the_brightness(self, qapp, tmp_path):
         prefs = Preferences(tmp_path)
         vis = VisualizerWidget(_FakePlayer(playing=True), prefs)
-        vis.mousePressEvent(None)        # Qt's first press: on -> dim
-        vis.mouseDoubleClickEvent(None)  # …which the double-click undoes
+        vis.open_big()          # Round 85: a single click on the tile
         try:
             assert vis._mode == MODE_ON
             assert prefs.get("visualizer_mode") == MODE_ON