refactor: change face trace display from 'F{id}' to 'Face{id}'

Problem:
- 'F13' display text confused with Frame numbers
- Users cannot distinguish between Trace ID and Frame Number

Solution:
- Change display format from 'F{trace_id}' to 'Face{trace_id}'
- Example: F13 → Face13, F142 → Face142

Changes:
- src/views/PeopleView.vue:264 - Cluster Detail Modal label

Benefits:
- Clear semantic meaning (Face vs Frame)
- No ambiguity for users
- Display layer only, data layer unchanged (still trace_id)

src/views/PeopleView.vue

@@ -261,7 +261,7 @@
                 <img v-if="faceThumbsCache[thumbTraceKey(t)]" :src="faceThumbsCache[thumbTraceKey(t)]" alt="" loading="lazy">
                 <div v-else style="width:100%;height:100%;display:flex;align-items:center;justify-content:center;background:#eef2ff;color:#6366f1;font-size:10px;font-weight:600;border-radius:8px;">F{{ t.trace_id }}</div>
               </div>
-              <div class="ms-ppl-strip-trace-label">F{{ t.trace_id }}<span class="ms-ppl-strip-group-name">{{ clusterDetailModal.cluster?.name }}</span></div>
+              <div class="ms-ppl-strip-trace-label">Face{{ t.trace_id }}<span class="ms-ppl-strip-group-name">{{ clusterDetailModal.cluster?.name }}</span></div>
             </div>
           </div>
           <button class="ms-ppl-strip-arrow" :disabled="clusterStripPage >= clusterStripTotalPages" @click="clusterStripPage++">›</button>