Test App Store review platform parsing

[cbusillo]

Summary

• replace the App Store review platform argparse source snapshot with direct parser behavior
• verify every runtime-supported target and metadata-source platform is accepted
• verify target defaults remain safe and unsupported, miscased, and empty values fail closed
• retain the existing tvOS workflow and copy-source wiring checks

Evidence

• 232 targeted submission/workflow tests passed
• all 10 routine Python lane files passed
• scripts/commit-gate.sh passed, including all 889 Swift tests
• Opus final amended review approved
• Gemini planning/final routes were invoked but returned no usable review text

Refs #579