Add automatic multi-format report generation and ZIP archiving

Implements automatic generation of JSON, HTML, and ZIP outputs after every scan,
with all files sharing the same timestamp for easy correlation.

Features:
- Automatic HTML report generation after every scan
- ZIP archive creation containing JSON, HTML, and all screenshots
- Unified timestamp across all outputs (JSON, HTML, ZIP, screenshots)
- Graceful error handling (scan continues if HTML/ZIP generation fails)
- Email-ready ZIP archives for easy sharing

Technical changes:
- Fixed timestamp mismatch between scan() and save_report()
- Added generate_outputs() method to SneakyScanner class
- scan() now returns (report, timestamp) tuple
- save_report() accepts timestamp parameter instead of generating new one
- main() updated to call generate_outputs() for all output formats
- Added zipfile import and HTMLReportGenerator import
- Dockerfile updated to copy templates/ directory

Output structure:
- scan_report_YYYYMMDD_HHMMSS.json (JSON report)
- scan_report_YYYYMMDD_HHMMSS.html (HTML report)
- scan_report_YYYYMMDD_HHMMSS.zip (archive with JSON, HTML, screenshots)
- scan_report_YYYYMMDD_HHMMSS_screenshots/ (screenshots directory)

Documentation updated:
- README.md: Updated Output Format, Features, Quick Start sections
- CLAUDE.md: Updated Core Components, Scan Workflow, Key Design Decisions

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

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

Dockerfile

@@ -32,6 +32,7 @@ RUN playwright install chromium
 
 # Copy application code
 COPY src/ ./src/
+COPY templates/ ./templates/
 
 # Create output directory
 RUN mkdir -p /app/output