Add code formatting implementation plan

Documents comprehensive plan for introducing Biome formatter with:
- Node.js v16 engine requirement update
- Biome installation and configuration
- Staged formatting rollout (lib/ first, then all files)
- Test suite validation at each stage
- Lefthook pre-commit hooks for automated formatting

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

Co-Authored-By: Claude <[email protected]>

Author: cressie176

todo.md

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+# Code Formatting Implementation Plan
+
+## Implementation Steps
+1. Update Node.js engine requirement to v16 (preparation for future test harness updates)
+2. Install Biome as development dependency
+3. Generate lib/defs.js using existing make target to ensure it is properly formatted
+4. Apply Biome formatting to all source code in lib/ directory
+5. Execute complete test suite to verify code changes maintain functionality
+6. Add npm format script to package.json for formatting lib/ directory
+7. Install and configure Lefthook with pre-commit hook to auto-format staged files
+8. Widen formatting scope to include all files and folders (not restricted to lib/)
+9. Apply Biome formatting to all files
+10. Execute complete test suite to verify all changes maintain functionality
+
+## Pull Request Structure
+<!-- Stackable PR organization will be defined here -->