Track CrossTL portability report compatibility

[NripeshN]

Summary

• extend the CrossTL project portability report schema and semantics with project unit, skipped unit, runtime-reference path, and artifact processing metadata
• add CrossTL #747/#831-inspired positive fixtures for source-remap and portability reports
• add negative coverage for migration runtime-reference path rollup mismatches
• harden runtime-loader plan CMake assertions for host-loader integration metadata

Validation

• cmake --build build --parallel "12"
• ctest --test-dir build --output-on-failure -R "(cglc_source_remap_v1_crosstl_pr747_demo_json_schema|cglc_crosstl_project_portability_report_v1_pr747_demo_json_schema|cglc_crosstl_project_portability_report_v1_mlx_arange_json_schema|cglc_invalid_json_schema_fixtures|cglc_shared_json_schema_defs|cglc_package_runtime_plan_directx_source_package_auto_schema|cglc_package_runtime_plan_vulkan_native_schema)" -j "12"
• ctest --test-dir build --output-on-failure -j "12"
• pre-commit run --all-files

Fixes #27