Convert issue forms to markdown templates

[mcdigman]

Summary

The YAML issue forms added in #24 render as a fixed form with no editable
body. That is more rigid than this project needs — a reporter cannot restructure
the report, drop an irrelevant section, or paste a shape the form did not
anticipate. This converts all four to classic Markdown templates, which prefill
the same guidance as an editable issue body.

What changed

• .github/ISSUE_TEMPLATE/0{1..4}_*.yml → .md, with name/about/title/labels frontmatter. Chooser entries, [bug] -style title prefixes, and auto-applied labels are unchanged; the forms' guidance survives as HTML comments, which do not render in the posted issue. Dropdowns became "delete all but one" lists.
• config.yml: dropped the Questions and help and Documentation contact links. A contact link navigates away from issue creation, so a "Documentation" entry opened the docs site rather than starting a docs issue — not what a chooser entry implies. Security vulnerability stays, since redirecting away from a public issue is exactly its intent.
• Two corrections carried in while rewriting: the adapter template no longer uses vulture as its example detector name (vulture already ships an adapter in liveness_primer/tools/vulture.py), and the corpus template spells out the SPDX allowlist inline instead of hiding it in a dropdown.

Verification

uv run prek run --all-files passes. Frontmatter on all four templates parses
as YAML with the expected keys:

01_bug_report.md        -> {'name': 'Bug report', 'title': '[bug] ', 'labels': 'bug'}
02_adapter_request.md   -> {'name': 'Detector adapter request', 'title': '[adapter] ', 'labels': 'adapter, enhancement'}
03_corpus_suggestion.md -> {'name': 'Corpus suggestion', 'title': '[corpus] ', 'labels': 'corpus'}
04_feature_request.md   -> {'name': 'Feature request', 'title': '[feature] ', 'labels': 'enhancement'}

All referenced labels (bug, adapter, enhancement, corpus) exist on the
repository. No file outside .github/ISSUE_TEMPLATE/ references the old .yml
paths.

Checklist

• uv run prek run --all-files passes locally.
• CHANGELOG.md entry skipped — repository metadata only, no packaged behavior change.

Tests, docstrings, and schema/corpus/explorer items do not apply: no Python
changed.

AI assistance

Claude Code performed the conversion and drafted the template prose; the
decision to move off issue forms and the contact-link removals are the
maintainer's, and the output was reviewed before commit.

Notes for the reviewer

Trade-off worth confirming: Markdown templates cannot require fields or vary
labels by answer, so version and reproduction details are now advisory. Given
that only description was actually required in the forms, this gives up
little enforcement in practice.

🤖 Generated with Claude Code