Prepare upstream workflow starters

[ehsanestaji]

Summary

• harden local nf-core starter metadata and test layout for upstream preparation
• add a workflow gate helper for collect-then-gate examples
• harden local Snakemake wrapper starter metadata and test layout
• document the safe order before external upstream PRs

Validation

• python3 -m unittest discover -s tests/python
• cargo test --locked
• git diff --check
• public naming scan