Implement Phase 1: enhanced HTML, JS blocks, and attribute syntax

Adds support for enhanced HTML tag embedding with !html[] syntax, JavaScript execution blocks using js-power code fences, and improved attribute syntax supporting key-value pairs, quoted values, and bare classes. Updates compiler/main.py with new processing functions and logic, extends documentation (user guide, changelog, phase1_features.md, phase1_summary.md, phase1_final_summary.md), and provides comprehensive examples and tests. Mark Phase 1 as complete in the roadmap and future enhancements plans.