chore: enforce PR-issue link via GH Actions

[brandonrc]

Summary

Adds .github/workflows/require-linked-issue.yml, which fails a PR check when the PR body does not reference an issue in this repo via Closes #N, Fixes #N, or Resolves #N (any tense, case-insensitive). The workflow uses actions/github-script@v7 to parse the body, verify the referenced issue exists, and post (or remove) a friendly bot comment explaining the policy. Maintainers can bypass with the no-issue-required label.

Closes #17
Refs artifact-keeper/artifact-keeper#1309

Part of the cross-repo rollout for the new PR-must-link-issue rule.

Test Checklist

• Spectral lint passes (no OpenAPI changes)
• All 5 SDK builds pass (no OpenAPI changes)
• No breaking changes
• Manually verified affected endpoints (none touched)

SDK Impact

• TypeScript SDK builds (unaffected)
• Kotlin SDK builds (unaffected)
• Swift SDK builds (unaffected)
• Rust SDK builds (unaffected)
• Python SDK builds (unaffected)
• Breaking change documented
• Version bump needed

[brandonrc]

Applied review fixes: switched to pull_request_target for fork support, added concurrency block, SHA-pinned actions/github-script, sanitize HTML comments and code blocks before regex, paginate listComments, surface 404 errors with specific issue number. Same canonical change pushed across all 8 enforcement PRs.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud