fix(codex-local): handle spawn error event in CodexRpcClient

When the `codex` binary is absent from PATH, Node.js emits an `error`
event on the ChildProcess. Because `CodexRpcClient` only subscribed to
`exit` and `data` events, the `error` event was unhandled — causing
Node to throw it as an uncaught exception and crash the server.

Add an `error` handler in the constructor that rejects all pending RPC
requests and clears the queue. This makes a missing `codex` binary a
recoverable condition: `fetchCodexRpcQuota()` rejects, `getQuotaWindows()`
catches the error and returns `{ ok: false }`, and the server stays up.

The fix mirrors the existing pattern in `runChildProcess`
(packages/adapter-utils/src/server-utils.ts) which already handles
`ENOENT` the same way for the main task execution path.

packages/adapters/codex-local/src/server/quota.ts

@@ -432,6 +432,13 @@ class CodexRpcClient {
       }
       this.pending.clear();
     });
+    this.proc.on("error", (err: Error) => {
+      for (const request of this.pending.values()) {
+        clearTimeout(request.timer);
+        request.reject(err);
+      }
+      this.pending.clear();
+    });
   }
 
   private onStdout(chunk: string) {