chore(ci): add CI workflow and Dependabot hardening

[t0kubetsu]

Summary

Add CI and Dependabot configuration to harden the repository.

Changes:

• ansible-lint on python:3.13-slim + github-actions Dependabot

Motivation

• No CI was running on this repo — lint/test regressions went undetected
• Dependency updates were manual — no automated security alerts
• Jobs run in minimal Debian-based containers instead of bare ubuntu-latest to reduce attack surface

Checklist

• CI workflow added
• Jobs run in containerised image (not bare ubuntu-latest)
• Dependabot configured