fix: remove auto-cleanup from DisposableProcess constructor

DisposableProcess should NOT auto-call dispose() on process 'close' event.
This was running cleanup before bash.ts finished reading streams.

Dispose is only called explicitly via timeout/abort handlers. Process streams
close naturally when process exits, so no forced cleanup is needed.

Author: ammar-agent

src/utils/disposableExec.ts

@@ -21,10 +21,8 @@ export class DisposableProcess implements Disposable {
   private disposed = false;
 
   constructor(private readonly process: ChildProcess) {
-    // Auto-cleanup when process exits
-    process.once("close", () => {
-      this[Symbol.dispose]();
-    });
+    // No auto-cleanup - callers explicitly dispose via timeout/abort handlers
+    // Process streams close naturally when process exits
   }
 
   /**