Add comprehensive database setup and user management system

- Implement PostgreSQL database schema with users and bookmarks tables
- Add database connection pooling with retry logic and error handling
- Create migration system with automatic schema initialization
- Add database CLI tools for management (init, status, validate, etc.)
- Include comprehensive error handling and diagnostics
- Add development seed data and testing utilities
- Implement health monitoring and connection pool statistics
- Create detailed documentation and troubleshooting guide

Database features:
- Users table with authentication fields and email verification
- Bookmarks table with user association and metadata
- Proper indexes for performance optimization
- Automatic timestamp triggers
- Transaction support with rollback handling
- Connection pooling (20 max connections, 30s idle timeout)
- Graceful shutdown handling

CLI commands available:
- npm run db:init - Initialize database
- npm run db:status - Check database status
- npm run db:validate - Validate schema
- npm run db:test - Run database tests
- npm run db:diagnostics - Full diagnostics

mobile_implementation_summary.md

@@ -0,0 +1,90 @@
+# Mobile Responsiveness and Touch Interactions Implementation Summary
+
+## Task 7: Enhance mobile responsiveness and touch interactions
+
+### ✅ Completed Sub-tasks:
+
+#### 1. Optimize touch targets for mobile devices (minimum 44px)
+- **Enhanced CSS for mobile breakpoints** (`@media (max-width: 768px)`)
+- **Button sizing**: All buttons now have `min-height: 44px` and `min-width: 44px`
+- **Touch-friendly inputs**: Form inputs have `min-height: 44px` and `font-size: 16px` (prevents iOS zoom)
+- **Bookmark items**: Increased to `min-height: 60px` with `padding: 16px 20px`
+- **Stats filters**: Enhanced to `min-height: 44px` with proper touch targets
+- **Close buttons**: Modal close buttons are now `44px x 44px` with centered content
+
+#### 2. Implement swipe gestures for bookmark actions on mobile
+- **Swipe detection**: Added touch event handlers (`touchstart`, `touchmove`, `touchend`)
+- **Swipe right**: Tests the bookmark link with visual feedback (green background)
+- **Swipe left**: Deletes the bookmark with confirmation (red background)
+- **Visual feedback**: CSS animations and color changes during swipe
+- **Swipe threshold**: 100px minimum distance required to trigger actions
+- **Touch state management**: Proper state tracking for touch interactions
+- **Swipe indicators**: SVG icons appear during swipe gestures (checkmark for test, trash for delete)
+
+#### 3. Add pull-to-refresh functionality for link testing
+- **Pull detection**: Touch handlers on main container for downward pulls
+- **Pull threshold**: 80px minimum pull distance to trigger refresh
+- **Visual indicator**: Dynamic pull-to-refresh indicator with progress feedback
+- **Smart refresh**: Tests invalid links first, or all links if none are invalid
+- **Scroll position check**: Only activates when at top of page (`window.scrollY === 0`)
+- **Visual feedback**: Indicator changes color and text based on pull progress
+
+#### 4. Optimize modal layouts for small screens
+- **Modal sizing**: Modals now use `width: 95%` and `max-height: 90vh` on mobile
+- **Stacked actions**: Modal buttons stack vertically with full width
+- **Enhanced close buttons**: Larger, more touch-friendly close buttons
+- **Form optimization**: Better spacing and sizing for form elements
+- **Content scrolling**: Proper overflow handling for long modal content
+- **Responsive headers**: Modal titles are centered and appropriately sized
+
+### 🔧 Technical Implementation Details:
+
+#### Mobile Detection
+```javascript
+isMobileDevice() {
+    return /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent) ||
+           ('ontouchstart' in window) ||
+           (navigator.maxTouchPoints > 0);
+}
+```
+
+#### Touch State Management
+- Tracks touch start/current positions
+- Manages swipe direction and threshold detection
+- Handles visual feedback states
+- Prevents conflicts with scrolling
+
+#### CSS Enhancements
+- **Touch action**: `touch-action: manipulation` for buttons
+- **Touch action**: `touch-action: pan-x` for swipeable items
+- **Touch action**: `touch-action: pan-y` for pull-to-refresh areas
+- **Visual feedback**: Active states with `transform: scale(0.95)` for touch feedback
+- **Swipe animations**: Smooth transitions for swipe gestures
+
+#### Accessibility Improvements
+- Maintained keyboard navigation alongside touch interactions
+- Proper ARIA labels and roles preserved
+- Screen reader compatibility maintained
+- High contrast ratios for visual feedback
+
+### 🧪 Testing
+- Created comprehensive test file: `test_mobile_interactions.html`
+- Tests swipe gestures with visual feedback
+- Tests pull-to-refresh functionality
+- Analyzes touch target sizes
+- Provides device information and interaction logging
+
+### 📱 Mobile-First Features
+1. **Enhanced touch targets**: All interactive elements meet 44px minimum
+2. **Swipe gestures**: Intuitive left/right swipes for common actions
+3. **Pull-to-refresh**: Natural mobile interaction for refreshing content
+4. **Responsive modals**: Optimized for small screens
+5. **Touch feedback**: Visual and haptic-like feedback for interactions
+6. **Gesture prevention**: Proper handling to prevent conflicts with browser gestures
+
+### 🎯 Requirements Satisfied
+- **Requirement 7.2**: Mobile responsiveness with touch-optimized interface
+- **Requirement 7.3**: Touch interactions with swipe gestures and pull-to-refresh
+- **Requirement 7.4**: Accessibility maintained with enhanced mobile support
+
+The implementation provides a native mobile app-like experience while maintaining full functionality and accessibility standards.