Test TestFlight platform behavior

[cbusillo]

Summary

• replace a whitespace-sensitive argparse.add_argument source snapshot with direct parser behavior tests
• verify TestFlight distribution requires --platform
• verify all four supported App Store Connect platforms parse and unsupported values fail closed

Evidence

• python3 -m unittest Tests/ScriptsTests/test_release_workflows.py Tests/ScriptsTests/test_distribute_testflight_beta.py — 147 passed
• python3 scripts/context-panel-test-lanes.py run --lane routine-ci-python — all 10 files passed
• scripts/commit-gate.sh — passed, including all 889 Swift tests
• Opus final review — approved
• Gemini review route — invoked repeatedly but returned no usable review text
• JetBrains changed-file inspection — unavailable because the worktree had no configured Python SDK

Refs #579