Track CrossTL project-porting report and source-remap compatibility

[NripeshN]

CrossTL PR CrossGL/crosstl#724 introduces repo-scale project-porting scaffolding around crosstl.toml, include/define forwarding, named variants, structured diagnostics, project reports, source maps, artifact manifests, and compiler-compatible source-remap sidecars.\n\nCompiler follow-up scope:\n- Track the CrossTL project report schema fields that compiler tooling may consume or validate.\n- Add fixtures for compiler-compatible source-remap sidecars emitted by CrossTL project translation.\n- Ensure existing cglc --source-remap validation accepts the compatible sidecar shape and rejects incompatible reports with useful diagnostics.\n- Keep this aligned with the shared CrossTL/CrossGL language contract snapshot after PR #724 lands.\n\nDo not mirror the full CrossTL project pipeline here unless compiler tools start consuming project reports directly.

[NripeshN]

Translator PR CrossGL/crosstl#724 currently emits file-level source maps, line-preserving mappings where the generated artifact keeps source line structure, and compiler-compatible source-remap sidecars for generated CrossGL artifacts. The remaining source-map bridge gap is backend/lowering span data: CrossTL can consume a stable compiler contract that exposes generated/original spans, mapping granularity (line/statement/token), source backend, target backend, and enough provenance to remap diagnostics after lowering. Until that exists, the translator should keep the project report schema practical and avoid claiming statement/token-level source maps for backend-generated output.