Improve issue and PR categories

[palewire]

Summary

Replace loose Markdown issue templates with structured GitHub issue forms that collect required details and automatically apply portable category labels. Add documentation and question forms, disable blank public issues, and make PR category and compatibility selection explicit.

Related Issue

N/A

Category

• Bug fix
• Feature
• Documentation
• Maintenance or refactor
• Dependency update

Compatibility

• This change is backward compatible.
• This change deprecates existing behavior.
• This change breaks existing behavior.

Validation

• pre-commit run --files ... — all applicable hooks passed
• Parsed every issue form as YAML and checked required top-level fields and unique field IDs
• git diff --check — passed

Checklist

• Tests cover the change, or no new tests are needed.
• Relevant edge cases are covered.
• Documentation is updated, or no update is needed.
• No changelog entry is needed for this contributor-workflow change.