ci: use GitHub App token for release-please

Use actions/create-github-app-token with GH_APP_ID / GH_APP_PRIVATE_KEY
so release-please commits are App-authored (Verified) and trigger CI,
unlike GITHUB_TOKEN which GitHub suppresses for workflow-initiated pushes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: louisgv

.github/workflows/release-please.yml

@@ -14,8 +14,15 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
+      - uses: actions/create-github-app-token@v2
+        id: app-token
+        with:
+          app-id: ${{ secrets.GH_APP_ID }}
+          private-key: ${{ secrets.GH_APP_PRIVATE_KEY }}
+
       - name: Run release-please
         uses: googleapis/release-please-action@v4
         with:
           config-file: release-please-config.json
           manifest-file: .release-please-manifest.json
+          token: ${{ steps.app-token.outputs.token }}