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/server/src/ws/handler.ts

@@ -15,6 +15,7 @@ import type {
   DmChannel,
   ServerEvent,
   SpaceFolder,
+  SpaceLayoutItem,
   ReadState,
   ActiveCallInfo,
 } from '@backspace/shared';
@@ -652,6 +653,7 @@ function buildReadyPayload(userId: string): {
   spaces: SpaceWithChannelsAndMembers[];
   dmChannels: DmChannel[];
   folders: SpaceFolder[];
+  spaceLayout: SpaceLayoutItem[] | null;
   voiceStates: Record<string, string[]>;
   voiceUserStates: Record<string, { isMuted: boolean; isDeafened: boolean; isCameraOn: boolean; isScreenSharing: boolean }>;
   spaceVoiceStates: Record<string, { spaceMuted: boolean; spaceDeafened: boolean; permissionMuted: boolean }>;
@@ -926,6 +928,7 @@ function buildReadyPayload(userId: string): {
     const folderSpaceIds = db.select()
       .from(schema.spaceFolderMembers)
       .where(eq(schema.spaceFolderMembers.folderId, folder.id))
+      .orderBy(schema.spaceFolderMembers.position)
       .all()
       .map(m => m.spaceId);
 
@@ -939,6 +942,11 @@ function buildReadyPayload(userId: string): {
     });
   }
 
+  // Get user space layout
+  const layoutRow = db.select().from(schema.userSpaceLayout)
+    .where(eq(schema.userSpaceLayout.userId, userId)).get();
+  const spaceLayout: SpaceLayoutItem[] | null = layoutRow ? JSON.parse(layoutRow.layout) : null;
+
   // Build voice states — tell the client who is currently in voice channels
   // across all their spaces
   const voiceStates: Record<string, string[]> = {};
@@ -1029,7 +1037,7 @@ function buildReadyPayload(userId: string): {
     lastReadMessageId: rs.lastReadMessageId,
   }));
 
-  return { user, spaces, dmChannels, folders, voiceStates, voiceUserStates, spaceVoiceStates, readStates, activeCalls };
+  return { user, spaces, dmChannels, folders, spaceLayout, voiceStates, voiceUserStates, spaceVoiceStates, readStates, activeCalls };
 }
 
 export async function registerWebSocket(app: FastifyInstance): Promise<void> {