feat: add semantic indexes for references and module hierarchy

[hongjr03]

Summary

• Move IDE semantic projections out of workspace symbols into a shared semantic index module.
• Keep references on definition-keyed semantic lookup instead of request-time text scanning.
• Add source-root module definition indexes plus resolved module instantiation edges, keyed internally by ModuleId, and use them for call hierarchy incoming/outgoing calls.

Validation

• cargo fmt --all -- --check
• cargo xtask check-config-artifacts
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace

[github-actions]

Docs preview: https://vide.pascal-lab.net/preview/pr-280/