Add comprehensive dark mode support with UI consistency fixes

This commit introduces a complete dark mode implementation across the entire application,
along with various UI consistency improvements and mobile responsiveness fixes.

Dark Mode Implementation:
- Added new dark-mode.css with comprehensive CSS variable system
- Implemented theme switcher with localStorage persistence
- Created dark mode color palette optimized for readability
- Added smooth transitions between light and dark themes

Component-Specific Dark Mode Styling:
- Headers: Added glowing gradient effects with animations (pulse, shimmer)
- Tables: Unified table styling across all views with proper dark mode support
- Forms: Updated all form controls, inputs, and buttons for dark mode
- Cards: Fixed white backgrounds in project cards, stat cards, and activity items
- Navigation: Enhanced sidebar and mobile navigation dark mode styling
- Modals: Added dark mode support for all modal dialogs including task modal
- Charts: Updated chart colors for dark mode visibility

UI Consistency Improvements:
- Standardized container padding (1rem) across all pages
- Unified page widths (regular: 1400px, admin: 1600px)
- Fixed mobile bottom navigation to only show on devices ≤768px
- Resolved page header positioning inconsistencies
- Improved text contrast ratios for better accessibility

Table Consolidation:
- Created tables-consolidated.css for unified table styling
- Removed duplicate table styles across components
- Standardized table headers, borders, and hover states
- Added responsive table behavior for mobile devices

Mobile Improvements:
- Fixed splash screen viewport coverage
- Enhanced mobile menu accessibility
- Improved touch targets for mobile interactions
- Added proper mobile-specific dark mode adjustments

Technical Details:
- CSS variables for easy theme customization
- Proper specificity management with [data-theme="dark"] selectors
- Performance optimized with minimal repaints
- Browser compatibility for modern browsers

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

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

static/css/style.css

@@ -284,7 +284,7 @@ button {
 
 .sidebar.collapsed .nav-icon {
     margin-right: 0;
-    font-size: 1.1rem;
+    font-size: 1.75rem;
 }
 
 /* Hide text in collapsed state */
@@ -1052,7 +1052,7 @@ input[type="time"]::-webkit-datetime-edit {
 .system-dashboard-container {
     max-width: 1600px;
     margin: 0 auto;
-    padding: 2rem;
+    padding: 1rem;
 }
 
 /* Common Admin Page Styles */