chore(deps): pin boneskull/gh-stack action to 4e39826

Author: renovate[bot]

.github/workflows/claude-code-review.yml

@@ -22,7 +22,7 @@ jobs:
       # Action definition is always fetched from main, so PRs that edit it
       # don't affect the running version until merged.
       - name: Run Claude Code Review
-        uses: boneskull/gh-stack/.github/actions/claude-code-review@main
+        uses: boneskull/gh-stack/.github/actions/claude-code-review@4e39826879db36f9b0e501d9d053a854674a61e3 # main
         with:
           claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
           repository: ${{ github.repository }}