feat(sessions): add stop confirmation, health checks, and tunnel recreation

- Add inline confirmation dialog before stopping instances
- Delete instances from state immediately without page reload
- Add health check polling every 30s for running instances
- Show tunnel error badge when tunnel is unreachable
- Add 'Fix Tunnel' button to recreate broken tunnels
- Update API client with health check and tunnel recreation endpoints

apps/web/src/styles.css

@@ -2611,9 +2611,17 @@ a.nav-item,
   align-items: center;
 }
 
-.delete-confirm-inline {
+.delete-confirm-inline,
+.stop-confirm-inline {
   display: flex;
   gap: var(--space-2);
+  align-items: center;
+}
+
+.confirm-text {
+  font-size: 13px;
+  color: var(--muted);
+  font-weight: 500;
 }
 
 .create-session-section {