Close frontend and Marketplace compatibility gaps

[lucamykael]

Summary

• close the remaining Mendix 10/11 native frontend compatibility gaps
• add fail-closed frontend schema/layout/design-property migration and reproducible acceptance gates
• add official Marketplace dependency resolution, transactional update/remove, widget installation, and protocol planning
• preserve assets, package originals, lock/cache provenance, native structures, and version-specific compiler seeds
• expose MxBuild zero-error validation and observable mx check diagnostics for source/rebuild

Validation

• 1,002 examples, 0 failures
• 100.00% lines (16,917/16,917)
• 100.00% branches (6,659/6,659)
• RuboCop: 238 files, 0 offenses
• git diff --check: clean
• Mendix 10.24.0.73019: source/rebuild frontend_ready, 0 MxBuild errors
• Mendix 11.12.1: source/rebuild frontend_ready, 0 MxBuild errors
• mx check source/rebuild signatures are identical:
  • 10.24: 0 errors, 173 package-owned warnings, 0 deprecations, 2 best-practice recommendations
  • 11.12: 0 errors, 10 package-owned warnings, 0 deprecations, 2 best-practice recommendations

The observable warnings belong to locked Marketplace modules; the round trip preserves them exactly and introduces no application-owned diagnostic drift.