release(v3): [2/4] Add support for return_run_details

[lasith-kg]

📚 PR Train

This PR is part of a stacked PR train delivering the v3 release. Review/merge bottom-up in order:

#	PR	Change	Base
1	#170	Modernize repository to actions/typescript (ESM + Node 24)	main
2	👉 #171 (this PR)	Add support for return_run_details	release/v3-1-node-24
3	#172	Remove dead error handling code	release/v3-2-dispatch-workflow
4	#173	v3 release (combined → main)	main

⚠️ PRs 1–3 are stacked (each targets the one above). PR #173 is the combined branch that actually merges into main.

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Uses GitHub's new return_run_details behaviour so workflow_dispatch gets the dispatched run's ID and URL straight from the API response — no more distinct-ID/run-name discovery workaround.

Highlights

• workflowDispatch reads run details from the dispatch response (return_run_details: true), returning { id, htmlUrl } directly.
• Discovery loop removed for workflow_dispatch — no distinct_id injection or run-listing/polling; that path is now repository_dispatch-only.
• Docs — README adds return_run_details background and a "Migrating from v2 to v3" section.

Depends on GitHub's return_run_details support — see the changelog announcement (2026-02-19; default from 2026-03-10). Existing run_id / run_url outputs are unchanged.