Visualizer: gray-mode color slider + mode persists across launches

- New prefs: visualizer_mode (on/dim/off, saved on every click) and
  color_visualizer_gray (None = keep the derived alternateBase look).
- VisualizerWidget takes prefs (optional, so existing call sites/tests
  keep working); restores its mode at startup and validates junk values.
- New "Visualizer (gray mode):" row in the Preferences color sliders;
  theme.default_gray mirrors the widget's 0.88-lightness derivation so
  an untouched slider shows the current appearance.
- TransportBar.refresh_theme() repaints the visualizer so slider drags
  preview live.

lintunes/gui/preferences_dialog.py

@@ -19,6 +19,7 @@ _COLOR_ROWS = [
     ("color_now_playing_bg", "Now-playing panel:"),
     ("color_now_playing_text", "Now-playing text:"),
     ("color_stripe", "Stripes:"),
+    ("color_visualizer_gray", "Visualizer (gray mode):"),
 ]
 
 

lintunes/gui/transport.py

@@ -255,7 +255,7 @@ class TransportBar(QWidget):
         layout.addWidget(shuffle_box)
 
         layout.addSpacing(10)
-        self._visualizer = VisualizerWidget(player)
+        self._visualizer = VisualizerWidget(player, prefs)
         self._visualizer.setFixedHeight(CONTROL_HEIGHT)
         layout.addWidget(self._visualizer)
         layout.addSpacing(10)
@@ -359,6 +359,7 @@ class TransportBar(QWidget):
             box.setStyleSheet(_box_style(box_bg))
         self._apply_now_playing_bg()
         self._apply_now_playing_font()
+        self._visualizer.update()  # dim-mode bar color may have changed
 
     def _apply_now_playing_bg(self):
         bg = theme.gray(theme.gray_value(self._prefs, "color_now_playing_bg"))

lintunes/gui/visualizer.py

@@ -11,6 +11,8 @@ from PyQt6.QtCore import Qt, QTimer, QRectF
 from PyQt6.QtGui import QPainter, QColor, QPainterPath, QPen
 from PyQt6.QtMultimedia import QAudioFormat
 
+from lintunes import theme
+
 
 BANDS = 20
 STEPS = 20          # vertical granularity per bar
@@ -41,10 +43,12 @@ class VisualizerWidget(QWidget):
     panel; off = blank.
     """
 
-    def __init__(self, player, parent=None):
+    def __init__(self, player, prefs=None, parent=None):
         super().__init__(parent)
         self._player = player
-        self._mode = MODE_ON
+        self._prefs = prefs
+        saved = prefs.get("visualizer_mode") if prefs is not None else None
+        self._mode = saved if saved in _MODE_CYCLE else MODE_ON
         self._levels = np.zeros(BANDS)
         self._bars = [0] * BANDS    # quantized 0..STEPS
         self._samples = np.zeros(FFT_SIZE, dtype=np.float32)
@@ -113,6 +117,8 @@ class VisualizerWidget(QWidget):
         # Cycle on -> dim -> off -> on.
         idx = _MODE_CYCLE.index(self._mode)
         self._mode = _MODE_CYCLE[(idx + 1) % len(_MODE_CYCLE)]
+        if self._prefs is not None:
+            self._prefs.set("visualizer_mode", self._mode)
         if self._mode == MODE_OFF:
             self._timer.stop()
             self._clear()  # off = blank, not the last frame held in place
@@ -150,6 +156,10 @@ class VisualizerWidget(QWidget):
 
     def _bar_color(self):
         if self._mode == MODE_DIM:
+            if self._prefs is not None:
+                saved = self._prefs.get("color_visualizer_gray")
+                if saved is not None:
+                    return theme.gray(saved)
             # Light gray just darker than the panel: take alternateBase and
             # drop its lightness ~12% so it tracks theme/scale changes.
             base = QColor(self.palette().alternateBase().color())