feat: add dev-workflow and forge-cli skills

Add two engineering skills for implementing tracker tickets end to end:

- dev-workflow: selects workflow:ready-for-agent tickets, runs them in
  isolated worktrees, opens one PR/MR per ticket, reviews, merges, and
  cleans up.
- forge-cli: detects the forge from origin and wraps gh, glab, and tea
  for Gitea/Forgejo, GitHub, and GitLab.

Docs cover install, prerequisites, ticket labels, and per-forge CLI usage.

docs/engineering/forge-cli.md

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