prepare(v0.2.3): robust tag-driven release workflow

[InitusNovus]

Prepare v0.2.3

This PR refines the Release workflow to prevent tag/package version mismatches and to make releases reproducible.

• Derive NuGet package version from tag (supports v/V prefixes)
• Validate version format before packing to avoid NuGet conflicts
• Support workflow_dispatch with explicit tag input; validates commit is on main
• Push only current-tag packages; verify artifacts exist

After merge:

• Create tag v0.2.3 on main
• Release workflow will pack/publish 0.2.3 and create GitHub Release