Test Ship workflow contracts semantically

[cbusillo]

Summary

• replace byte-offset Ship workflow assertions with scoped job and step contract helpers
• verify release-channel dependency wiring and exhaustive App Store platform preflight mapping
• preserve TestFlight source/channel validation and no-review policy without pinning harmless YAML formatting

Refs #579

Validation

• python3 -m unittest Tests/ScriptsTests/test_release_workflows.py (129 passed)
• python3 scripts/context-panel-test-lanes.py run --lane routine-ci-python
• scripts/commit-gate.sh (including 889 Swift tests)
• mutation probes for missing validation dependency, unmapped platform, and harmless job reordering
• Opus and Gemini exact-SHA final reviews approved 0519804

Inspection

• JetBrains changed-files inspection was inconclusive because IntelliJ has no Python SDK configured for this worktree; no actionable findings were returned.