Fix V06 release availability check

[sufyanaser]

Root cause

The release workflow used gh release view to probe whether v6.0.0 existed. On the current Windows runner, the expected non-zero result for a missing release terminated the PowerShell step before its conditional logic could mark the tag as publishable.

Fix

• Query the GitHub Releases API with Invoke-WebRequest -SkipHttpErrorCheck.
• Treat HTTP 200 as an existing release.
• Treat HTTP 404 as available for publication.
• Fail closed for all unexpected API status codes.

Verification

• Lint: passed
• TypeScript: passed
• Tests: 61/61 passed
• Production build: passed
• Diff/status/log checks: passed