teach deploy: port safety & DX enhancements from quick-deploy.sh

[Data-Wise]

Summary

Port 4 battle-tested safety and DX features from STAT-545's quick-deploy.sh into teach deploy. These are additive improvements — no breaking changes on the happy path. CI mode remains fully non-interactive.

Enhancements

1. Trap Handler for Branch Safety

trap "git checkout '$draft_branch'" EXIT INT TERM in both direct merge and PR modes. Guarantees return to draft branch on any error/signal instead of relying on manual checkout in each error path.

2. GitHub Actions Monitoring Link

Add Actions: line to the deploy summary box, showing https://github.com/<owner>/<repo>/actions. Extracted from remote.origin.url. Skipped for non-GitHub remotes.

3. Pre-Commit Hook Failure Recovery

When git commit fails during deploy (likely pre-commit hook), show actionable 3-option recovery:

1. Fix issues, re-run teach deploy
2. Skip validation: QUARTO_PRE_COMMIT_RENDER=0 teach deploy ...
3. Force commit: git commit --no-verify -m "message"

4. Uncommitted Changes Prompt (Direct Mode)

Instead of blocking with "working tree dirty", prompt to commit with a smart message. CI mode still fails fast.

Acceptance Criteria

• Trap handler returns to draft branch on any error/signal in both modes
• Deploy summary box includes GitHub Actions URL
• Pre-commit hook failures show actionable recovery message
• teach deploy -d with uncommitted changes prompts to commit
• --ci mode: uncommitted changes fail, hook failures exit non-zero
• All existing tests pass unchanged
• New tests cover trap, hook failure, uncommitted prompt paths

Spec

See docs/specs/SPEC-teach-deploy-safety-2026-02-08.md on dev branch.

Version Target

v6.6.0

[Data-Wise]

Shipped in v6.6.0 via PR #366 (feat: teach deploy safety & DX enhancements).