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>

server/internal/tenant/app/desktop_account_service.go

@@ -656,8 +656,8 @@ func resolveDesktopClientOnline(
 	if client == nil || client.RevokedAt != nil {
 		return false
 	}
-	if presenceKnown && presence {
-		return true
+	if presenceKnown {
+		return presence
 	}
 	if client.LastSeenAt == nil {
 		return false