UOW-006: Add Package Documentation and API Documentation

[andhijeannot]

Overview

Phase: 2 - Code Quality
Priority: High
Estimated Effort: 6-8 hours

Problem Description

The codebase lacks comprehensive documentation with most packages missing package-level documentation comments and exported functions lacking godoc comments.

Acceptance Criteria

• All packages have comprehensive package-level documentation
• All exported functions and types have godoc comments
• Code examples included for major functionality
• Architecture decisions documented
• API usage guide created
• Documentation follows Go conventions

Files to Modify

• All packages in internal/ (add documentation)
• docs/architecture/ (new ADR documents)
• docs/API.md (new API documentation)
• examples/ (new code examples)

See roadmap/phase2-quality/UOW-006-documentation.md for detailed implementation plan.