docs: issue templates, PR templates, and CONTRIBUTING.md

[simonteague6]

Summary

This PR introduces 3 issue templates, a PR template, and updates the CONTRIBUTING.md. It also disables blank issue templates.

Why

It provides a standard way of writing issues, in a very simple and readable format. This enables everyone to create issues, because it makes it much simpler and easier. It also forces AI to use the same format, making issue creation with AI reliable. PR templates also help document what the author actually contributed, giving them a chance to explain what they did, like I am doing here.

Related issue

Closes #67

What changed

• created bug issue template
• created feature issue template
• created chore issue template
• created PR template
• rewrote CONTRIBUTING.md entirely

How it was tested

• Ran the current committed versions through Ajv in strict mode against SchemaStore's github-issue-forms.json: bug.yml, feature.yml, chore.yml all pass with zero warnings
• I also had AI compare the issue template forms against the official docs (form schema reference + issue forms config)

just check result

• just check passes locally (matches CI)

Data or schema impact

N/A (no data/schema impact)

Deployment or rollback considerations

N/A

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Author checklist

• Linked to one issue with a closing keyword (Closes #…, Fixes #…, or Resolves #…)
• PR title uses Conventional Commit style (e.g. feat:, fix:, docs:) so the squashed commit is clear
• Related tests updated and passing
• just check passes and CI is green
• Screenshots/recordings included for UI changes
• just validate-data run for graph-data changes
• I understand and can explain every change in this PR (including AI-written code)

[SamuelSaylor]

beautiful