feat(preproc): add queryable preprocessor model

[hongjr03]

Summary

• Split the preproc crate into explicit index and model modules.
• Add a queryable preprocessor model built on source-order events and macro environment replay.
• Expose macro visibility, macro definition/reference resolution, provenance, includes, and inactive branch facts through hir::preproc.
• Wire IDE completion, go to definition, hover, and references to structured preprocessor facts for macros, conditional macro tokens, and literal includes.

Scope

• Covers single-file macro environments with manifest predefines.
• Keeps IDE consumers behind the HIR preprocessor facade.
• Leaves full include-chain macro replay and manifest source-range provenance for follow-up work.

Validation

• cargo test -p preproc
• cargo test -p ide preproc_macro -- --nocapture
• 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/