fix: resume draft releases by exact tag

[jinyounghub]

What changed

• Fall back from GitHub's published-only tag endpoint to the authenticated paginated release list in both draft staging and final publication.
• Require a case-sensitive exact tag match, reject duplicates, and fail with explicit errors when a draft cannot be found.
• Keep a static contract requiring both release jobs to retain the draft lookup path.
• Record the fix under Unreleased without changing the already published 0.2.3 version.

Why

The v0.2.3 workflow created and uploaded the exact 16-asset draft successfully, but GET /releases/tags/v0.2.3 returned 404 because GitHub documents that endpoint as returning published releases. The authenticated release list does include drafts for tokens with push access. Both jobs need the fallback: staging resumes drafts after an interruption, and the final job must read the same draft before publishing it.

Validation

• verify-version-sync.ps1
• git diff --check
• Live regression probe using a temporary v0.2.2 draft:
  • tag endpoint returned the documented 404
  • paginated authenticated list returned exactly the draft ID with draft: true
  • temporary draft deleted immediately; tag unchanged
• v0.2.3 post-release workflow, assets, NuGet package, Marketplace, and Pages independently verified