feat: broadcast full CRDT state to other clients after manual save

When a user saves, the full Yjs document state is broadcast so all
connected clients converge, even if they missed incremental updates.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/collaboration/crdt.ts

@@ -173,6 +173,17 @@ export class CRDTManager {
     this.callbacks.onEdgesChange(this.getEdges())
   }
 
+  /** Broadcast the full document state to sync all connected clients */
+  broadcastFullState(): void {
+    if (!this.channel || this.isDestroyed) return
+    const fullState = Y.encodeStateAsUpdate(this.doc)
+    this.channel.send({
+      type: 'broadcast',
+      event: BROADCAST_EVENT,
+      payload: { update: Array.from(fullState) },
+    })
+  }
+
   private broadcastUpdate(update: Uint8Array): void {
     if (!this.channel || this.isDestroyed) return
     this.channel.send({