Fix semantic highlighting for locals shadowing crate names

[zakazaka95]

Summary

• prioritize function-local pattern lookup before crate/module resolution during semantic highlighting
• add regression coverage for a local snforge_std binding shadowing the crate name

This keeps the local declaration and its use classified as variables instead of namespaces.

Verification

• added an end-to-end semantic-token regression test
• git diff --check
• the Rust test suite was not run locally because this environment has no Rust toolchain; CI should execute the new regression

Closes #1302