## Summary
- add a reusable skill for the Dependabot PR rollup workflow
- place it under `.agents/skills/` for cross-client discovery
- keep the skill aligned with the Agent Skills standard and
client-agnostic

## Details
- adds `.agents/skills/dependabot-pr-rollup/SKILL.md`
- documents the workflow for:
  - finding open Dependabot PRs
  - comparing PR heads to their base branch
  - replaying only net dependency changes in a fresh worktree
  - running `npm run all`
  - optionally committing, pushing, and opening a PR

## Notes
- `.agents/skills/` is the shared interoperability location used across
multiple coding agents
- no code changes
- tests not run (documentation-only skill)

## Summary
- replace the root `AGENTS.md` symlink with a real file
- move the agent instructions out of `.github/copilot-instructions.md`
into `AGENTS.md`
- trim the content down to concise, repo-specific guidance and add a
short repository orientation

## Testing
- not run (docs-only change)

Closes: #777
Closes: #325