Add daily cleanup for stale copilot/ branches

[Copilot]

Adds a scheduled workflow to prune copilot/ branches that have gone inactive for more than 24 hours. This keeps short-lived agent branches from accumulating while preserving recently active work.

• Workflow

  • Adds .github/workflows/daily-copilot-branch-cleaner.md with a daily schedule and manual trigger.
  • Compiles the workflow to .github/workflows/daily-copilot-branch-cleaner.lock.yml.

• Branch cleanup behavior

  • Enumerates refs under refs/heads/copilot/.
  • Reads the head commit timestamp for each branch and treats the most recent author/committer time as last activity.
  • Deletes only branches whose last activity is at least 24 hours old.

• Operational visibility

  • Emits a step summary with per-branch outcomes: deleted, kept, skipped, or failed.
  • Fails the run if any deletion attempt errors so cleanup problems surface instead of being silently ignored.

on:
  schedule:
    - cron: "17 3 * * *"
  workflow_dispatch:

jobs:
  cleanup_copilot_branches:
    permissions:
      contents: write

if (ageHours < 24) {
  results.push({ branch, action: 'kept' });
} else {
  await github.rest.git.deleteRef({ owner, repo, ref: `heads/${branch}` });
}