feat: enforce 100% frame-based positioning (no time)

Core Principle: Frame is the ONLY standard

Changes:
- VideoPlayer: Remove startTime/endTime props
- VideoPlayer: Add mandatory startFrame/endFrame check
- VideoPlayer: UI shows F123 (51.2s) format
- All Views: Only set startFrame/endFrame
- All Views: Only pass :start-frame/:end-frame
- Remove all startTime/endTime from currentVideo refs

Time is only used for display (auxiliary).
Frame is the source of truth for all positioning.

src/components/VideoPlayer.vue

@@ -139,7 +139,7 @@
           <span class="ms-video-seg-info2">{{ currentItemIdx + 1 }} / {{ totalItems }}</span>
           <button class="ms-fm-btn ms-video-nav-btn" @click="nextItem" :disabled="!canNext">下一個 &rarr;</button>
         </div>
-        <span v-else class="ms-video-seg-info">{{ formatTime(currentTime) }} / {{ formatTime(duration) }}</span>
+        <span v-else class="ms-video-seg-info">F{{ currentFrame }} / F{{ totalFrames }} <span class="ms-video-time-aux">({{ formatTime(currentTime) }} / {{ formatTime(duration) }})</span></span>
       </div>
     </div>
   </div>
@@ -159,10 +159,8 @@ const zIndexValue = ref(getNextZIndex())
 
 const props = withDefaults(defineProps<{
   fileUuid: string
-  startTime?: number
-  endTime?: number
-  startFrame?: number
-  endFrame?: number
+  startFrame: number
+  endFrame: number
   allTraces?: any[]
   mergedSegments?: any[]
   initialTraceIdx?: number
@@ -171,6 +169,8 @@ const props = withDefaults(defineProps<{
   simple?: boolean
   useOriginal?: boolean
 }>(), {
+  startFrame: 0,
+  endFrame: 0,
   allTraces: () => [],
   mergedSegments: () => [],
   initialTraceIdx: 0,
@@ -888,17 +888,20 @@ onMounted(async () => {
     emit('trace-change', currentTraceIdx.value)
   } else {
     try {
-      const params: any = {
+      if (props.startFrame == null || props.endFrame == null) {
+        videoError.value = 'ERROR: startFrame and endFrame are required'
+        videoLoading.value = false
+        return
+      }
+      
+      const data = await apiCall('get_video_stream', {
         uuid: props.fileUuid,
+        startTime: null,
+        endTime: null,
+        startFrame: props.startFrame,
+        endFrame: props.endFrame,
         original: props.useOriginal,
-      }
-      
-      if (props.startFrame != null && props.endFrame != null) {
-        params.startFrame = props.startFrame
-        params.endFrame = props.endFrame
-      }
-      
-      const data = await apiCall('get_video_stream', params)
+      })
       if (typeof data === 'string') {
         videoSrc.value = data
       } else {
@@ -970,7 +973,8 @@ onUnmounted(() => {
 .ms-video-tl-pos-tip { display: none; position: absolute; bottom: 20px; left: 50%; transform: translateX(-50%); background: #1a56db; color: #fff; font-size: 10px; padding: 2px 6px; border-radius: 4px; white-space: nowrap; pointer-events: none; z-index: 10; }
 .ms-video-tl-position:hover .ms-video-tl-pos-tip { display: block; }
 .ms-video-nav { display: flex; align-items: center; justify-content: space-between; margin-top: 14px; gap: 10px; flex-wrap: wrap; }
-.ms-video-seg-info { font-size: 12px; color: rgba(255,255,255,0.6); flex-shrink: 0; }
+.ms-video-seg-info { font-size: 12px; color: rgba(255,255,255,0.9); flex-shrink: 0; font-weight: 500; }
+.ms-video-time-aux { font-size: 11px; color: rgba(255,255,255,0.5); margin-left: 6px; }
 .ms-video-seg-info2 { font-size: 12px; color: #9aa0a6; flex: 1; text-align: center; }
 
 /* Frame seek controls */