feat(stats): wire stats server, overlay, and CLI into main process

- Stats server auto-start on immersion tracker init
- Stats overlay toggle via keybinding and IPC
- Stats CLI command (subminer stats) with cleanup mode
- mpv plugin menu integration for stats toggle
- CLI args for --stats, --stats-cleanup, --stats-response-path

src/main/runtime/mpv-client-event-bindings.test.ts

@@ -75,6 +75,7 @@ test('mpv event bindings register all expected events', () => {
     onMediaPathChange: () => {},
     onMediaTitleChange: () => {},
     onTimePosChange: () => {},
+    onDurationChange: () => {},
     onPauseChange: () => {},
     onSubtitleMetricsChange: () => {},
     onSecondarySubtitleVisibility: () => {},
@@ -95,6 +96,7 @@ test('mpv event bindings register all expected events', () => {
     'media-path-change',
     'media-title-change',
     'time-pos-change',
+    'duration-change',
     'pause-change',
     'subtitle-metrics-change',
     'secondary-subtitle-visibility',