refactor(preproc): add preprocessor query model

[hongjr03]

Summary

• Split the preprocessor crate into explicit index and model modules.
• Add a query-oriented preprocessor model for macro visibility, usage resolution, provenance, includes, and conditional branch access.
• Update downstream imports to use the explicit preproc::index module path.

Validation

• cargo test -p preproc
• cargo check -p hir
• cargo check -p ide
• cargo fmt --check
• git diff --check

[github-actions]

Docs preview: https://vide.pascal-lab.net/preview/pr-228/