Problem: existing tests asserted that `parse.body()` stripped forge
tokens from the description and populated `meta.forge_ref`. The
`conceal_patterns` test referenced a removed function.
Solution: update `parse.body` integration tests to assert tokens stay
in the description. Add `find_refs()` tests covering single/multiple
refs, URLs, byte offsets, and empty cases. Remove `conceal_patterns`
test. Update diff tests to assert description includes the token.
Problem: no test coverage for forge link shorthand parsing, URL
parsing, label formatting, or API URL generation.
Solution: add `spec/forge_spec.lua` covering `_parse_shorthand`,
`parse_ref` for all three forges, full URL parsing including nested
GitLab groups, `format_label`, and `_api_url`.
