chore(ci): add stale action for old Issues/PRs (NVIDIA#1581)

Adds a once-per-day action for marking PRs/Issues as stale

| Type  | Notification | Close    | Label-to-Skip  |
|:------|:-------------|:--------:|:--------------:|
| Issue | 60 days      | +7 days  | `Needs Triage` |
| PR    | 30 days      | +14 days | `Under Review` |

Closes

## By Submitting this PR I confirm:
- I am familiar with the [Contributing Guidelines](https://github.com/NVIDIA/NeMo-Agent-Toolkit/blob/develop/docs/source/resources/contributing/index.md).
- We require that all contributors "sign-off" on their commits. This certifies that the contribution is your original work, or you have rights to submit it under the same license, or a compatible license.
  - Any contribution which contains commits that are not Signed-Off will not be accepted.
- When the PR is ready for review, new or existing tests cover these changes.
- When the PR is ready for review, the documentation is up to date with these changes.



## Summary by CodeRabbit

* **Chores**
  * Added an automated daily repository workflow to mark and close stale issues and pull requests. Configured inactivity thresholds and timelines (issue stale/close and PR stale/close), custom messages for stale and closed states, and exemptions for specified labels to prevent automated actions on items under active review.

Authors:
  - Will Killian (https://github.com/willkill07)

Approvers:
  - https://github.com/mnajafian-nv

URL: NVIDIA#1581

Author: willkill07

.github/workflows/stale.yaml

@@ -0,0 +1,36 @@
+# SPDX-FileCopyrightText: Copyright (c) 2025-2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: 'Close stale issues and PRs'
+on:
+  schedule:
+    - cron: '0 12 * * *'
+
+jobs:
+  stale:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/stale@v10
+        with:
+          stale-issue-message: 'This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 7 days.'
+          stale-pr-message: 'This PR is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 14 days.'
+          close-issue-message: 'This issue was closed because it has been stalled for 7 days with no activity.'
+          close-pr-message: 'This PR was closed because it has been stalled for 14 days with no activity.'
+          days-before-issue-stale: 60
+          days-before-issue-close: 7
+          days-before-pr-stale: 30
+          days-before-pr-close: 14
+          exempt-issue-labels: 'Needs Triage'
+          exempt-pr-labels: 'Under Review'