refactor(kling): 优化时长匹配逻辑，使用固定阈值替代比例计算

frontend/app/web-gold/src/views/kling/components/TimelinePanel.vue

@@ -135,10 +135,13 @@ const isExceed = computed(() => props.audioDurationMs > props.faceDurationMs)
 
 const diffMs = computed(() => Math.abs(props.audioDurationMs - props.faceDurationMs))
 
+/** 时长差异阈值：3秒内视为匹配 */
+const MATCH_THRESHOLD_MS = 3000
+
 const diffStatus = computed(() => {
   if (props.audioDurationMs === 0) return 'none'
   if (props.audioDurationMs > props.faceDurationMs) return 'exceed'
-  if (props.audioDurationMs < props.faceDurationMs * 0.5) return 'short'
+  if (props.faceDurationMs - props.audioDurationMs > MATCH_THRESHOLD_MS) return 'short'
   return 'match'
 })
 

frontend/app/web-gold/src/views/kling/stores/useDigitalHumanStore.ts

@@ -156,7 +156,7 @@ export const useDigitalHumanStore = defineStore('digitalHuman', () => {
     if (!timeline.value || timeline.value.audioDurationMs === 0) return 'none'
     const { videoDurationMs, audioDurationMs } = timeline.value
     if (audioDurationMs > videoDurationMs) return 'exceed'
-    if (audioDurationMs < videoDurationMs * 0.3) return 'too-short'
+    if (videoDurationMs - audioDurationMs > 3000) return 'too-short'
     return 'match'
   })