fix: enforce frame-based positioning across all video playback

Core Principle: Frame is the only standard

Changes:
- VideoPlayer: Add startFrame/endFrame props
- VideoPlayer: Use frame parameters in simple playback path
- SearchView: Remove frame/time conversion (stop using fps = 24)
- PeopleView: Pass frames directly instead of time
- PersonDetailView: Pass frames directly instead of time

All video streams now use startFrame/endFrame API parameters.
Time conversion only happens in VideoPlayer internals for UI display.

Ref: frame-based positioning standards research

src/components/VideoPlayer.vue

@@ -161,6 +161,8 @@ const props = withDefaults(defineProps<{
   fileUuid: string
   startTime?: number
   endTime?: number
+  startFrame?: number
+  endFrame?: number
   allTraces?: any[]
   mergedSegments?: any[]
   initialTraceIdx?: number
@@ -886,10 +888,15 @@ onMounted(async () => {
     emit('trace-change', currentTraceIdx.value)
   } else {
     try {
-      const st = props.startTime ?? 0
-      pendingSeekTime.value = st
+      const stFrame = props.startFrame ?? 0
+      const enFrame = props.endFrame
+      
       const data = await apiCall('get_video_stream', {
         uuid: props.fileUuid,
+        startTime: null,
+        endTime: null,
+        startFrame: stFrame,
+        endFrame: enFrame,
         original: props.useOriginal,
       })
       if (typeof data === 'string') {

src/views/PeopleView.vue

@@ -1060,8 +1060,8 @@ async function playClusterVideo() {
     
     currentVideo.value = {
       fileUuid,
-      startTime: firstTrace ? (firstTrace.start_frame / fps) : 0,
-      endTime: lastTrace ? (lastTrace.end_frame / fps) : 30,
+      startFrame: firstTrace ? firstTrace.start_frame : 0,
+      endFrame: lastTrace ? lastTrace.end_frame : 30,
       title: `${getFileName(fileUuid)} - ${c.name}`,
     }
     clusterVideoTraces.value = allClusterTraces
@@ -1083,8 +1083,8 @@ async function playClusterTraceVideo(trace: any) {
     
     currentVideo.value = {
       fileUuid,
-      startTime: startFrame / fps,
-      endTime: endFrame / fps,
+      startFrame: startFrame,
+      endFrame: endFrame,
       title: `${getFileName(fileUuid)} - F${trace.trace_id}`,
     }
     clusterVideoTraces.value = [{

src/views/PersonDetailView.vue

@@ -443,8 +443,8 @@ function playTrace(t: any) {
   const endFrame = (t.last_frame || 0) + 10
   currentVideo.value = {
     fileUuid: t.file_uuid || '',
-    startTime: startFrame / fps,
-    endTime: endFrame / fps,
+    startFrame: startFrame,
+    endFrame: endFrame,
     traceIdx: idx,
     title: `${person.value?.name} · T${t.trace_id}`,
   }

src/views/SearchView.vue

@@ -805,11 +805,8 @@ function formatTime(sec: number): string {
 function playVideo(r: any) {
   const sf = r.start_frame || 0
   const ef = r.end_frame || sf + 1
-  const fps = 24
   currentVideo.value = {
     fileUuid: r.file_uuid,
-    startTime: sf / fps,
-    endTime: ef / fps,
     startFrame: sf,
     endFrame: ef,
     title: r.summary?.slice(0, 60) || r.file_name || 'Video'