docs: update CLAUDE.md and add contribution guidelines

[LudoLoops]

Issue

Now that we have comprehensive analysis of the codebase structure (CLAUDE.md), we should document:

1. Contributing guidelines
2. Code style expectations
3. Common refactoring patterns
4. Performance considerations

Current State

• ✓ CLAUDE.md exists (great!)
• ✓ ANALYSIS.md exists (bug/optimization list)
• ✗ No CONTRIBUTING.md
• ✗ No architecture decision records
• ✗ No developer setup guide

Solution

Create/Update:

CONTRIBUTING.md

• How to set up development environment
• Running tests
• Code style (Go conventions)
• PR process
• Issue types and labels

developer-guide.md

• Common patterns in codebase
• How to add new commands
• How to add new config options
• Performance tips

Benefits

• Lower barrier to contribution
• Consistent code quality from contributors
• Clear expectations

Impact

🟢 Low - Documentation only