feat(player): add frame counter when scrubbing and seeking

Show a timecode + frame readout above the timeline while dragging the
playhead, and flash it for a moment on keyboard/button seeks so frame
stepping is visible too.

Position and text are written from the existing rAF/DOM path that drives
the playhead, so the readout stays smooth without extra React renders.

Two supporting fixes the count depends on:

- Seed the frame rate from the HLS manifest FRAME-RATE attribute so a
  frame number is available before playback ever starts; previously the
  rate was only ever measured from requestVideoFrameCallback and stayed
  null until the video had played.
- Snap the measured rate to the nearest broadcast standard and skip
  samples taken mid-seek. A drifting float slid the count by whole
  frames late in a long video, and re-publishing a slightly different
  float on every presented frame forced a re-render per video frame.

components/video-page-content.tsx

@@ -90,6 +90,7 @@ export function VideoPageContent({
   const timelineRef = useRef<HTMLDivElement>(null);
   const progressRef = useRef<HTMLDivElement>(null);
   const playheadRef = useRef<HTMLDivElement>(null);
+  const scrubReadoutRef = useRef<HTMLDivElement>(null);
   const videoContainerRef = useRef<HTMLDivElement>(null);
   const pathname = usePathname();
   const scheduleWatchProgressSaveRef = useRef<
@@ -322,6 +323,7 @@ export function VideoPageContent({
     isMuted,
     isFrameMode,
     frameStepLabel,
+    showScrubReadout,
     playbackSpeed,
     qualityOptions,
     selectedQualityLevel,
@@ -357,8 +359,10 @@ export function VideoPageContent({
     timelineRef,
     progressRef,
     playheadRef,
+    scrubReadoutRef,
     hlsRef,
     playerRef,
+    formatTime,
     formatBunnyQualityLabel,
     speedOptions: SPEED_OPTIONS,
     scheduleWatchProgressSaveRef,
@@ -783,7 +787,9 @@ export function VideoPageContent({
             timelineRef={timelineRef}
             progressRef={progressRef}
             playheadRef={playheadRef}
+            scrubReadoutRef={scrubReadoutRef}
             videoContainerRef={videoContainerRef}
+            showScrubReadout={showScrubReadout}
             isFullscreenMode={isFullscreenMode}
             cursorIdle={cursorIdle}
             isPlaying={isPlaying}