Add release tag helper

[austin-smith]

What Changed

• Add a guarded release tag helper with stable, prerelease, and dry-run modes.
• Validate release tags against the Xcode marketing version before signing begins.
• Document the concise release commands and configuration references.

Why

Creating release tags manually can publish a tag from the wrong commit, use a mismatched version, or overwrite an existing release. The helper and workflow validation make the tag-driven release process safer and repeatable.

Validation

• SwiftLint passed.
• Unsigned iOS build passed.
• All 223 macOS tests passed.
• Stable and prerelease dry-runs passed in a disposable repository.
• Duplicate-tag and non-main commit rejection passed.
• Workflow stable, prerelease, malformed-tag, and version-mismatch checks passed.
• YAML parsing, shell syntax, and git diff checks passed.