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

server/internal/tenant/app/desktop_account_service_test.go

@@ -21,15 +21,27 @@ func TestResolveDesktopClientOnline_PresenceHitWins(t *testing.T) {
 	assert.True(t, online)
 }
 
-func TestResolveDesktopClientOnline_FallsBackToRecentHeartbeatWhenPresenceMisses(t *testing.T) {
+func TestResolveDesktopClientOnline_PresenceMissWithKnownPresenceIsOffline(t *testing.T) {
 	now := time.Date(2026, 4, 19, 21, 30, 0, 0, time.UTC)
-	lastSeen := now.Add(-30 * time.Second)
+	lastSeen := now.Add(-desktopClientPresenceTTL / 2)
 
 	online := resolveDesktopClientOnline(&repository.DesktopClient{
 		ID:         uuid.New(),
 		LastSeenAt: &lastSeen,
 	}, false, true, now)
 
+	assert.False(t, online)
+}
+
+func TestResolveDesktopClientOnline_FallsBackToRecentHeartbeatWhenPresenceUnknown(t *testing.T) {
+	now := time.Date(2026, 4, 19, 21, 30, 0, 0, time.UTC)
+	lastSeen := now.Add(-desktopClientPresenceTTL / 2)
+
+	online := resolveDesktopClientOnline(&repository.DesktopClient{
+		ID:         uuid.New(),
+		LastSeenAt: &lastSeen,
+	}, false, false, now)
+
 	assert.True(t, online)
 }
 

server/internal/tenant/app/desktop_presence.go

@@ -10,10 +10,10 @@ import (
 )
 
 // desktopClientPresenceTTL is also used as the monitoring primary-client lease TTL.
-// Desktop heartbeat interval must stay below TTL/2, so one missed heartbeat does
-// not make another client eligible to steal a still-healthy primary lease.
-const desktopClientPresenceTTL = 90 * time.Second
-const desktopAccountPresenceTTL = 90 * time.Second
+// Desktop heartbeat interval is TTL/2, so unexpected client exits are reflected
+// as offline within one TTL even when the explicit offline request is missed.
+const desktopClientPresenceTTL = 30 * time.Second
+const desktopAccountPresenceTTL = 30 * time.Second
 
 func desktopClientPresenceKey(clientID uuid.UUID) string {
 	return "desktop:presence:client:" + clientID.String()