Admit source annotations on the via-index compile path

[gunbai-bot]

Summary

• The floor's via-index parse (resolved_graph_from_sources_with_index) used annotation-erasing tokenize, so a touched in-closure file could compile while missing SourceAnnotationRefused — the class Restore whole-tree census fill on scoped compile-clean gate #8204 claims to close. The ordinary frontend already admits via tokenize_artifact + admit_source_annotations; via-index now does the same for the files it actually compiles.
• Out-of-closure census fill (Restore whole-tree census fill on scoped compile-clean gate #8204) now runs independently of resolve, so an earlier resolution refusal cannot hide the annotation population.
• Warm parse_cache stores those admission diagnostics on the installing parse. handle_serve resolves Memoize, consumes compile_clean_diags, and shares process_shared_index, so re-admission is no longer gated on Ephemeral.
• Restore whole-tree census fill on scoped compile-clean gate #8204 stays as the differential oracle. This PR does not delete it.

Test plan

• cargo test -p v1-compiler --lib compile_clean_via_index_verdict_equivalence — including:
  • in-closure BodyGrain RED on via-index (census_only empty, so Restore whole-tree census fill on scoped compile-clean gate #8204 cannot explain it)
  • in-closure UnattachedAtScopeEnd RED on via-index
  • leading item prose stays green
  • in-closure BodyGrain still visible when resolve also refuses
  • out-of-closure trailing still visible when resolve also refuses
  • warm parse_cache still reds on in-closure BodyGrain (Ephemeral then Ephemeral)
  • Ephemeral then Memoize (handle_serve shape: parse_cache hit, memo miss) still reds BodyGrain
  • annotation-erasing parse_cache install then Memoize still reds BodyGrain
  • existing Restore whole-tree census fill on scoped compile-clean gate #8204 out-of-closure trailing RED and green/unresolved/typecheck equivalence