Add sloccount.html tool with WebPerl integration and comprehensive tests (#75)

This commit adds a new mobile-friendly web tool for analyzing source code
line counts using the Perl sloccount tool via WebAssembly.

Features:
- Mobile-responsive UI with tab-based interface
- Support for pasted code with language detection based on file extension
- Support for GitHub repository analysis via GitHub API
- WebPerl integration for running Perl code in the browser
- Real-time line counting with filtering of comments and empty lines
- Language breakdown with visual table display
- Comprehensive Playwright test suite with 12 test cases

Also includes TOOLS_GUIDE.md documentation for repository patterns and
development guidelines.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: simonw