feat(ui): rename 图生图→参考图 with count; distinguish video 首尾帧 vs 参考图

- model list: any model with max_reference_images>0 shows 首尾帧 N (frame mode)
  or 参考图 N (asset/other); drop the count-less "图生图" label
- ModelFormModal / TestModal: capability labels use 参考图 (not 图生图)
- grok-video uses reference_mode=asset (参考图), runway/adobe video stay frame (首尾帧)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/ModelFormModal.vue

@@ -241,8 +241,8 @@ async function save() {
                   <span v-for="r in resolutions" :key="r" class="ro-chip">{{ r }}</span>
                   <span v-if="!resolutions.length" class="text-white/30">—</span>
                 </div>
-                <span class="text-white/40">图生图</span>
-                <div class="text-white/70">{{ entry.image_to_image ? '支持' : '不支持' }}</div>
+                <span class="text-white/40">参考图</span>
+                <div class="text-white/70">{{ entry.max_reference_images > 0 ? `${entry.max_reference_images} 张` : (entry.image_to_image ? '支持' : '不支持') }}</div>
               </template>
             </div>
           </div>