Phase 3 Step 1: Fix Styling Issues & CSS Refactor

Extracted inline CSS to external stylesheet and fixed white row bug
affecting dynamically created table rows across all scan views.

Changes:
- Created web/static/css/styles.css with extracted CSS from base.html
- Added CSS variables for consistent theming and maintainability
- Added Bootstrap 5 CSS variable overrides to fix table styling
- Integrated Chart.js 4.4.0 for future dashboard visualizations
- Added Bootstrap Icons for enhanced UI components

Template Updates:
- Updated base.html to use external CSS instead of inline styles
- Added Chart.js dark theme configuration
- Fixed white row bug in dashboard.html (added .scan-row class)
- Fixed white row bug in scans.html (added .scan-row class)
- Fixed white row bug in scan_detail.html port tables (added .scan-row class)

The white row bug was caused by Bootstrap 5's CSS variables overriding
custom styles. Fixed by setting --bs-table-bg and related variables.

Phase 3 Documentation:
- Added PHASE3.md with complete implementation plan (2204 lines)
- Includes 8 implementation steps, file changes, and success criteria

This completes Phase 3 Step 1 (Day 1 of 14).

web/templates/dashboard.html

@@ -224,6 +224,7 @@
 
         scans.forEach(scan => {
             const row = document.createElement('tr');
+            row.classList.add('scan-row');  // Fix white row bug
 
             // Format timestamp
             const timestamp = new Date(scan.timestamp).toLocaleString();