Migrate pipeline lint rules to AST-grep

[edmundmiller]

Stack child of #4377.

Moves the pipeline/workflow lint examples onto AST-grep rule files: ifEmpty(null), TODO comments, and System.exit checks.

No subworkflow-specific changes here; subworkflow TODO lint delegates to the same shared pipeline TODO helper.

Stack

1. Bump tree-sitter-nextflow parser pin #4378
2. Add AST-grep lint foundations #4377
3. Migrate pipeline lint rules to AST-grep #4381 👈 current
4. Flag legacy versions.yml topic outputs #4379
5. Flag legacy versions emits #4380

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.10%. Comparing base (9500344) to head (1a08623).

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.