perf: fix memory leaks — strip task outputs from SSE broadcasts, use light state everywhere

- TaskTracker.getTaskTreeLight(): strips large `output` strings from tasks
  in SSE broadcasts (was serializing 5-10MB every 500ms with many subagents)
- session:created broadcasts now use toLightDetailedState() (consistent with
  session:updated which already did)
- GET /api/sessions/:id returns light state (no 2-3MB terminal+text buffers)
- Ralph wizard polls /terminal?tail=2048 instead of full session endpoint

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/task-tracker.ts

@@ -547,6 +547,27 @@ export class TaskTracker extends EventEmitter {
     return rootTasks;
   }
 
+  /**
+   * Lightweight task tree for SSE broadcasts — strips large `output` strings
+   * to avoid serializing 5-10MB of task results every 500ms.
+   * Full task details available via getTaskTree().
+   *
+   * @returns Array of root tasks with output truncated to 200 chars
+   */
+  getTaskTreeLight(): Omit<BackgroundTask, 'output'>[] {
+    const rootTasks: Omit<BackgroundTask, 'output'>[] = [];
+
+    for (const task of this.tasks.values()) {
+      if (!task.parentId) {
+        // Strip output to avoid serializing large strings on every broadcast
+        const { output: _output, ...lightTask } = task;
+        rootTasks.push(lightTask);
+      }
+    }
+
+    return rootTasks;
+  }
+
   /**
    * Get all tasks as a flat Map.
    *