feat: space sidebar drag-and-drop reordering with folder system

Add user_space_layout table and PUT /api/users/@me/space-layout endpoint
for persisting per-user sidebar ordering. Spaces can be freely reordered
via drag-and-drop, folders created by dragging one space onto another,
and folders auto-dissolve when they have fewer than 2 members. Includes
folder context menu (rename, color, ungroup), collapsed folder mini-grid
icons, multi-tab sync via WebSocket, and localStorage collapse state.
Removes the rigid native/federated split — federated spaces now intermix
freely while keeping their globe badge.

packages/web/src/hooks/useWebSocket.ts

@@ -107,7 +107,7 @@ function handleEvent(origin: string, event: ServerEvent): void {
         }
       }
 
-      populateFromReady(origin, event.spaces, event.folders, event.dmChannels);
+      populateFromReady(origin, event.spaces, event.folders, event.dmChannels, event.spaceLayout);
 
       // Cache authoritative identity for this origin (federation-safe)
       if (!isHome) {
@@ -697,6 +697,14 @@ function handleEvent(origin: string, event: ServerEvent): void {
       break;
     }
 
+    case 'space_layout_updated': {
+      if (!isHome) break;
+      const { setSpaceLayout } = useSpaceStore.getState();
+      setSpaceLayout(event.layout);
+      useSpaceStore.setState({ folders: event.folders });
+      break;
+    }
+
     // ─── Join request events (home-only) ────────────────────────────────
 
     case 'join_request_received': {