feat(queue): collapse ReplayGain into a click-to-expand badge

Per @cucadmuh's feedback: the presence of ReplayGain matters more than
the actual numbers. The tech bar now shows a small 'RG' pill on line 1
whenever the track has any RG metadata; hovering reveals the values via
tooltip, clicking persistently expands the second line.

- Source icon stays inline before the format string (was getting
  separated from FLAC by the centred stack layout)
- Pill uses --accent-tinted color-mix so it adapts to every theme
- ChevronDown rotates on expand for a clear affordance
- New persisted state: themeStore.expandReplayGain (default collapsed)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/store/themeStore.ts

@@ -24,6 +24,8 @@ interface ThemeState {
   setShowBitrate: (v: boolean) => void;
   showRemainingTime: boolean;
   setShowRemainingTime: (v: boolean) => void;
+  expandReplayGain: boolean;
+  setExpandReplayGain: (v: boolean) => void;
 }
 
 export function getScheduledTheme(state: Pick<ThemeState, 'enableThemeScheduler' | 'theme' | 'themeDay' | 'themeNight' | 'timeDayStart' | 'timeNightStart'>): string {
@@ -63,6 +65,8 @@ export const useThemeStore = create<ThemeState>()(
       setShowBitrate: (v) => set({ showBitrate: v }),
       showRemainingTime: false,
       setShowRemainingTime: (v) => set({ showRemainingTime: v }),
+      expandReplayGain: false,
+      setExpandReplayGain: (v) => set({ expandReplayGain: v }),
     }),
     {
       name: 'psysonic_theme',