Add workspace symbol alias regression coverage

[partyplatter08-lab]

Summary

• add a workspace-symbol regression test that builds a vault with YAML frontmatter aliases and verifies an alias query returns a FILE symbol
• keep the workspace-symbol matcher clippy-clean while preserving existing scoring behavior
• clean up small existing clippy warnings so strict local linting passes

Validation

• cargo fmt --check
• cargo test
• cargo clippy --all-targets -- -D warnings
• cargo check

/claim #263