[TRUNK-17581] Improve Merge Queue API reference with examples and cross-links

[samgutentag]

Summary

Improves the Merge Queue public API reference page with better discoverability, practical guidance, and cross-linking to related documentation.

Changes

• Endpoint summary table — Quick-reference table listing all 10 API endpoints with anchor links for fast navigation
• Common use cases section — Practical guidance for CI/CD automation, monitoring dashboards, queue state management, parallel queue configuration, and test monitoring
• Authentication section — Expanded auth docs including forked PR authentication via x-forked-workflow-run-id header
• Additional curl examples — Added PR status check example alongside existing submit/cancel examples; fixed request body format to use proper pr.number field
• Endpoint descriptions — Added contextual descriptions for getSubmittedPullRequest, setImpactedTargets, getMergeQueueTestingDetails, and deleteQueue
• Related resources section — Links to CLI reference, parallel queues API, webhooks, queue settings, and authentication docs
• Consistent formatting — Horizontal rules between sections, proper heading hierarchy

Related

• Resolves TRUNK-17581
• Related to TRUNK-16666 (Update Merge Queue Public API docs)
• Changelog: https://trunk.io/changelog/merge-queue-public-api-for-queue-management

Test plan

• Verify OpenAPI spec blocks render correctly in GitBook preview
• Confirm anchor links in endpoint summary table resolve to correct sections
• Check cross-reference links to CLI reference, parallel queues, webhooks, and settings pages
• Verify collapsible example blocks render properly
• Confirm the deleteQueue warning hint renders correctly
• Verify forked PR auth info hint renders as an info block