chore(claude): add CLAUDE.md

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 personal VSCode configuration repository (vscode-siren) that provides
+a unified configuration for VSCode-based editors including Cursor, VSCode,
+VSCode Insiders, and Windsurf. It focuses on recreating an Emacs-like text
+editor experience with custom keybindings, settings, and extensions.
+
+## Key Commands
+
+### Configuration Management
+
+- `./siren <editor> config` - Create symlinks for editor config files
+- `./siren <editor> extensions` - Install extensions from lock file
+- `./siren <editor> extensions --latest` - Install latest versions of extensions
+- `./siren <editor> dump-extensions` - Export installed extensions to lock file
+
+### Makefile Shortcuts
+
+- `make cursor-config` - Configure Cursor editor
+- `make cursor-extensions` - Install Cursor extensions
+- `make all-config` - Configure all editors
+- `make all-extensions` - Install extensions for all editors
+
+### Supported Editors
+
+- `cursor` (c) - Cursor editor
+- `vscode` (code, vsc, v) - Visual Studio Code
+- `vscode-insiders` (vsci, i) - Visual Studio Code Insiders
+- `windsurf` (surf, w) - Windsurf editor
+
+## Architecture
+
+### Core Components
+
+- **siren script** - Main configuration management tool (bash script)
+- **settings.json** - VSCode settings configuration
+- **keybindings.json** - Custom keybindings (Emacs-inspired)
+- **snippets/** - Code snippets for Go and Ruby
+- **extensions.*.lock** - Extension lock files for each editor
+
+### Configuration Structure
+
+- Config files are symlinked to appropriate editor directories based on OS
+- Extensions are managed via lock files with version pinning
+- Cursor uses .vsix installation due to signature verification issues
+- Static symlinks for additional files like cspell dictionary and MCP config
+
+### Key Features
+
+- Cross-platform support (macOS/Linux)
+- Version-locked extensions with fallback to .vsix downloads
+- Automatic backup of existing configurations
+- Emacs-inspired keybindings and workflow
+- Dark/light theme switching based on system preferences
+
+## Development Guidelines
+
+Based on cursor/user-rules.md:
+
+- Keep line length to 80 characters when possible
+- Check Makefile for common project tasks
+- Be direct and terse in communication
+- Provide code solutions rather than general advice
+- Include robust error handling
+- Consider cross-platform compatibility
+- Respect existing code comments