chore: add CLAUDE.md with project guidelines

.gitignore

@@ -5,7 +5,7 @@ target/
 
 # Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
 # More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
-Cargo.lock
+#Cargo.lock
 
 # These are backup files generated by rustfmt
 **/*.rs.bk
@@ -21,3 +21,4 @@ Cargo.lock
 #.idea/
 .mentat
 .ai-commit.json
+.DS_Store

CLAUDE.md

@@ -0,0 +1,21 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build/Lint/Test Commands
+- Build: `cargo build [--release]`
+- Lint: `cargo clippy -- -D warnings`
+- Format: `cargo fmt --all -- --check`
+- Test: `cargo test`
+- Test single: `cargo test -p <package_name> <test_name>`
+- Run tool: `cargo run -p <package_name> -- <arguments>`
+
+## Code Style Guidelines
+- **Imports**: Standard library first, external crates alphabetically second, modules last
+- **Formatting**: Follow standard Rust formatting (4-space indentation)
+- **Types**: Explicitly type function parameters and return types; use PathBuf for file paths
+- **Naming**: snake_case for variables/functions, CamelCase for types/structs
+- **Error Handling**: Prefer Result<T> over unwrap()/expect(); include context in error messages
+- **CLI**: Use clap with derive feature for argument parsing; document with /// comments
+- **Concurrency**: Use Rayon for CPU-bound tasks; Tokio for I/O-bound operations
+- **Resources**: Ensure proper cleanup of file handles, network connections, progress bars