Add HTML report generation with dark theme

Implements comprehensive HTML report generation from JSON scan data with Jinja2 templates. Reports feature a dark slate theme with summary dashboard, drift alerts, security warnings, and expandable service details.

Features:
- Dark theme HTML reports with slate/grey color scheme
- Summary dashboard: scan statistics, drift alerts, security warnings
- Site-by-site breakdown with IP grouping and status badges
- Expandable service details and SSL/TLS certificate information
- Visual badges: green (expected), red (unexpected), yellow (missing)
- UDP port handling: shows expected, unexpected, and missing UDP ports
- Screenshot links with relative paths for portability
- Optimized hover effects for table rows
- Standalone HTML output (no external dependencies)

Technical changes:
- Added src/report_generator.py: HTMLReportGenerator class with summary calculations
- Added templates/report_template.html: Jinja2 template for dynamic reports
- Added templates/report_mockup.html: Static mockup for design testing
- Updated requirements.txt: Added Jinja2==3.1.2
- Updated README.md: Added HTML report generation section with usage and features
- Updated CLAUDE.md: Added implementation details, usage guide, and troubleshooting

Usage:
  python3 src/report_generator.py output/scan_report.json

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

Co-Authored-By: Claude <noreply@anthropic.com>

requirements.txt

@@ -2,3 +2,4 @@ PyYAML==6.0.1
 python-libnmap==0.7.3
 sslyze==6.0.0
 playwright==1.40.0
+Jinja2==3.1.2