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/scan_detail.html

@@ -306,12 +306,13 @@
                 const ports = ip.ports || [];
 
                 if (ports.length === 0) {
-                    portsContainer.innerHTML = '<tr><td colspan="7" class="text-center text-muted">No ports found</td></tr>';
+                    portsContainer.innerHTML = '<tr class="scan-row"><td colspan="7" class="text-center text-muted">No ports found</td></tr>';
                 } else {
                     ports.forEach(port => {
                         const service = port.services && port.services.length > 0 ? port.services[0] : null;
 
                         const row = document.createElement('tr');
+                        row.classList.add('scan-row');  // Fix white row bug
                         row.innerHTML = `
                             <td class="mono">${port.port}</td>
                             <td>${port.protocol.toUpperCase()}</td>