refactor: remove waveform color setting to preserve dynamic coloring

- Removed waveformColor from UISettings interface
- Removed waveform color picker from Interface settings tab
- Preserves dynamic per-track waveform coloring system
- Cleaner settings UI with one less option

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

components/settings/GlobalSettingsDialog.tsx

@@ -375,29 +375,6 @@ export function GlobalSettingsDialog({
                   </p>
                 </div>
 
-                {/* Waveform Color */}
-                <div className="space-y-2">
-                  <label className="text-sm font-medium">Waveform Color</label>
-                  <div className="flex gap-2 items-center">
-                    <input
-                      type="color"
-                      value={settings.ui.waveformColor}
-                      onChange={(e) => onUISettingsChange({ waveformColor: e.target.value })}
-                      className="h-10 w-20 rounded border border-border cursor-pointer"
-                    />
-                    <input
-                      type="text"
-                      value={settings.ui.waveformColor}
-                      onChange={(e) => onUISettingsChange({ waveformColor: e.target.value })}
-                      className="flex-1 px-3 py-2 bg-background border border-border rounded text-sm font-mono"
-                      placeholder="#3b82f6"
-                    />
-                  </div>
-                  <p className="text-xs text-muted-foreground">
-                    Default color for new track waveforms.
-                  </p>
-                </div>
-
                 {/* Font Size */}
                 <div className="space-y-2">
                   <label className="text-sm font-medium">Font Size</label>