Add webpage screenshot capture with Playwright

Implements automated screenshot capture for all discovered HTTP/HTTPS services using Playwright with headless Chromium. Screenshots are saved as PNG files and referenced in JSON reports.

Features:
- Separate ScreenshotCapture module for code organization
- Viewport screenshots (1280x720) with 15-second timeout
- Graceful handling of self-signed certificates
- Browser reuse for optimal performance
- Screenshots stored in timestamped directories
- Comprehensive documentation in README.md and new CLAUDE.md

Technical changes:
- Added src/screenshot_capture.py: Screenshot capture module with context manager pattern
- Updated src/scanner.py: Integrated screenshot capture into HTTP/HTTPS analysis phase
- Updated Dockerfile: Added Chromium and Playwright browser installation
- Updated requirements.txt: Added playwright==1.40.0
- Added CLAUDE.md: Developer documentation and implementation guide
- Updated README.md: Enhanced features section, added screenshot details and troubleshooting
- Updated .gitignore: Ignore entire output/ directory including screenshots

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

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

requirements.txt

@@ -1,3 +1,4 @@
 PyYAML==6.0.1
 python-libnmap==0.7.3
 sslyze==6.0.0
+playwright==1.40.0