perf: improve terminal batching for snappier UI response

Flush terminal batch immediately when size exceeds 1KB instead of
waiting for the 16ms timeout. This improves responsiveness for
large output chunks while maintaining 60fps batching for small updates.

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

src/web/server.ts

@@ -1347,11 +1347,23 @@ export class WebServer extends EventEmitter {
   }
 
   // Batch terminal data for better performance (60fps)
+  // Flushes immediately if batch > 1KB for snappier response to large outputs
   private batchTerminalData(sessionId: string, data: string): void {
     const existing = this.terminalBatches.get(sessionId) || '';
-    this.terminalBatches.set(sessionId, existing + data);
+    const newBatch = existing + data;
+    this.terminalBatches.set(sessionId, newBatch);
 
-    // Start batch timer if not already running
+    // Flush immediately if batch is large (>1KB) for responsiveness
+    if (newBatch.length > 1024) {
+      if (this.terminalBatchTimer) {
+        clearTimeout(this.terminalBatchTimer);
+        this.terminalBatchTimer = null;
+      }
+      this.flushTerminalBatches();
+      return;
+    }
+
+    // Start batch timer if not already running (16ms = 60fps)
     if (!this.terminalBatchTimer) {
       this.terminalBatchTimer = setTimeout(() => {
         this.flushTerminalBatches();