chore(github): add issue and pull request templates

[decode2]

Linked issue

Closes #28

• The linked issue has the status:approved label.

Pull request type

Select exactly one option and apply the matching type:* label.

• Bug fix (type:bug)
• New feature (type:feature)
• Documentation (type:docs)
• Refactor (type:refactor)
• Maintenance or tooling (type:chore)
• Breaking change (type:breaking-change)

Summary

• Bootstraps feature and bug issue forms plus a pull request template for future issue-first pull requests.
• Requires maintainer approval and consistent pull request classification without altering product runtime.

Changes

Area or file	Change
.github/ISSUE_TEMPLATE/bug_report.yml	Adds the structured bug report form.
.github/ISSUE_TEMPLATE/feature_request.yml	Adds the structured feature request form.
.github/ISSUE_TEMPLATE/config.yml	Disables blank issues.
.github/PULL_REQUEST_TEMPLATE.md	Adds approved-issue linkage, type selection, test evidence, chain context, and contributor checks.

Test plan

• Ran the focused automated checks: git diff --cached --check passed before commit; pre-commit, pre-push, and pre-PR review gates allowed review lineage review-9fc5416d34409fc9, generation 1.
• Exercised the affected terminal, AI CLI, or desktop workflow: Not applicable; this change only adds GitHub governance metadata and does not alter product runtime.
• Verified relevant Windows, Linux, or WSL behavior, or documented why it is not applicable: Not applicable; GitHub consumes these repository files independently of product operating system.

Chained pull request context

• Previous PR: Not applicable
• Next PR: Not applicable
• Review this PR first: The required issue fields, approval contract, exact PR type selection, and contributor checklist.
• Intentionally out of scope: Contributor label permissions and the current CONTRIBUTING policy mismatch are known informational follow-ups from the approved review.

Contributor checklist

• I searched for duplicate issues and pull requests before starting.
• I linked an approved issue using Closes, Fixes, or Resolves.
• I selected exactly one pull request type and applied exactly one matching type:* label.
• I completed every relevant template field and included reproducible test evidence.
• I updated documentation when behavior or compatibility changed.
• My commits follow Conventional Commits.
• My commits contain no AI attribution, including Co-Authored-By trailers.