feat(FN-3843): add chat stream reattach support

Adds the changeset for FN-3843, completing the chat stream reattach feature for the `@runfusion/fusion` CLI package.

Fusion-Task-Id: FN-3843

packages/dashboard/src/chat.ts

@@ -1225,6 +1225,13 @@ export class ChatManager {
     return this.activeGenerations.has(sessionId);
   }
 
+  /**
+   * Return the active generation ID for a session, if any.
+   */
+  getActiveGenerationId(sessionId: string): number | undefined {
+    return this.activeGenerations.get(sessionId)?.generationId;
+  }
+
   /**
    * Return all session IDs that currently have an active generation.
    * Useful for batch-enriching session lists without N+1 lookups.