feat: tighten desktop presence loop and refine admin-web UX

- Shrink desktop presence TTL to 30s and heartbeat to 15s so unexpected
  client exits surface within one TTL even if the explicit offline call
  is missed; keep migration default aligned.
- Trust a known presence miss in resolveDesktopClientOnline instead of
  falling back to the recent-heartbeat heuristic, so a still-cached
  LastSeenAt cannot mask an offline client.
- Release the runtime session before clearing renderer desktop sessions
  on shutdown to avoid leaving stale leases behind.
- Auto-refresh the MediaView account list every 5s and revamp card
  layout (inline platform badge, status tags, UID row, meta box).
- Let the brand-question AI wizard accept multiple seed topics via a
  tag-style input; candidates from each topic are merged and deduped.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/i18n/messages/en-US.ts

@@ -1403,6 +1403,9 @@ const enUS = {
       ai: {
         note: 'AI expansion consumes 1 AI point. Failed generations are refunded automatically.',
         seedTopic: 'Seed topic',
+        seedTopicPlaceholder: 'Enter a topic and press Enter; multiple topics supported',
+        seedTopicHint:
+          'Use Enter, commas, or semicolons to add multiple topics. Candidates are merged and deduplicated automatically.',
         generate: 'Generate with AI',
         waitingTitle: 'AI is generating candidate questions. Please wait...',
         waitingStages: {

apps/admin-web/src/i18n/messages/zh-CN.ts

@@ -1331,6 +1331,8 @@ const zhCN = {
       ai: {
         note: "AI 扩展会消耗 1 个 AI 点；生成失败时系统会自动退还。",
         seedTopic: "扩展主题",
+        seedTopicPlaceholder: "输入主题后按回车，可添加多个",
+        seedTopicHint: "支持回车、逗号或分号分隔多个主题；系统会逐个扩展并自动合并去重。",
         generate: "AI 生成候选",
         waitingTitle: "AI 正在生成候选问题，请稍后…",
         waitingStages: {