Add custom release artifact names

[kelindi]

Summary

• Add an optional artifact-name input for custom published DMG or ZIP filenames.
• Preserve the existing one-pass release path when the input is omitted.
• Extract release orchestration into a testable Bash helper and cover default, DMG, ZIP, and invalid-name paths.

Why

Releases built directly from an Xcode project currently use Amore's product-derived artifact name. Consumers that need a versioned or otherwise custom download filename have no way to name the generated artifact before it is uploaded.

When artifact-name is set, the action now builds the signed/notarized artifact locally with --output, renames it, and publishes that existing artifact. Build-only flags stay on the first invocation, while release metadata and channel flags stay on the publishing invocation.

Validation

• bash -n scripts/release.sh tests/release_test.sh
• tests/release_test.sh
• Parsed action.yml with Ruby YAML
• git diff --check