update to modern tooling

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is a Go CLI tool for validating and fixing files according to .editorconfig rules. The tool provides four main commands: `check`, `fix`, `ls`, and `rules`.
+
+## Development Commands
+
+- **Build**: `go build -o editorconfig-cli .` (creates single binary)
+- **Run tests**: `go test ./editorconfig`
+- **Cross-platform build**: Use `bin/build` script (requires fixing Go path)
+- **Test the CLI**:
+    - `./editorconfig-cli check [paths]` - validate files
+    - `./editorconfig-cli fix [paths]` - fix files
+    - `./editorconfig-cli ls [paths]` - list matched files
+    - `./editorconfig-cli rules [paths]` - show rules for files
+
+## Modern Setup
+
+This project has been modernized with Go modules. The original `bin/build` script uses a hardcoded Go path (`/usr/local/go/bin/go`) that may not exist on modern systems. Use `go build` directly instead.
+
+## Architecture
+
+The main application entry point is in `main.go`, which delegates to the CLI app created in `editorconfig/cli.go`. The core functionality is organized into:
+
+- **Command handlers**: `*_command.go` files implement the four main CLI commands
+- **Rule processing**: `line_checkers.go`, `line_fixers.go`, `full_file_checkers.go`, `full_file_fixers.go` contain the validation and fixing logic
+- **File discovery**: `source_file_finder.go` handles finding files to process
+- **Configuration**: `config_file_finder.go` and `config_file.go` handle .editorconfig file parsing
+- **Path matching**: `path_matcher.go` implements glob pattern matching for .editorconfig sections
+
+## Key Implementation Details
+
+- The project uses the `github.com/codegangsta/cli` library for command-line interface
+- Rules are applied based on .editorconfig files found in the directory hierarchy
+- The tool supports standard .editorconfig properties: `indent_style`, `indent_size`, `tab_width`, `end_of_line`, `charset`, `trim_trailing_whitespace`, `insert_final_newline`
+- File pattern matching supports most glob patterns, with some limitations documented in `path_matcher.go`
+
+## Testing
+
+All Go packages have corresponding `*_test.go` files. The test suite includes both unit tests and integration tests using sample files in `editorconfig/tests/`.