ci(github): use app token for dependabot merges

[ncipollina]

Summary

Updates the Dependabot auto-merge workflow to use the LayeredCraft GitHub App token for approving and enabling auto-merge. This avoids using GITHUB_TOKEN for the merge operation so downstream workflows can run after Dependabot auto-merged changes land on main.

Changes

• Adds a SHA-pinned actions/create-github-app-token step for semver patch/minor Dependabot PRs.
• Uses the generated app token as GH_TOKEN for gh pr review --approve and gh pr merge --auto --squash.
• Keeps dependabot/fetch-metadata on the default GITHUB_TOKEN.

Validation

• Reviewed workflow syntax and token usage.
• No build required; workflow-only change.

Notes for Reviewers

Requires the Actions secrets DEPENDABOT_AUTOMERGE_APP_ID and DEPENDABOT_AUTOMERGE_PRIVATE_KEY to be available to this repository.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid secrets in Dependabot pull_request_target runs

Because this job is restricted to dependabot[bot] pull_request_target events, these newly referenced app credentials are not available in the run; GitHub's secret-type docs state that Dependabot-initiated pull_request_target workflows receive a read-only GITHUB_TOKEN and no secrets (https://docs.github.com/en/code-security/reference/secret-security/secret-types#dependabot-secrets). As a result, actions/create-github-app-token will receive empty app credentials and fail before the approval/auto-merge steps for every eligible Dependabot patch/minor PR. Use a hand-off workflow under a non-Dependabot actor or another supported credential path.

Useful? React with 👍 / 👎.

[j-d-ha]

LGTM