Extract Query Strings to Separate Files

[lexasub]

Difficulty: ⭐⭐ Medium
Files: ast_rag/language_queries.py
Description: Move tree-sitter query strings to separate .s-exp files for better maintainability.
Steps:

1. Create queries/java/, queries/cpp/, etc.
2. Move query strings to .s-exp files
3. Load queries at runtime