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

.kiro/specs/bookmark-manager/tasks.md

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+# Implementation Plan
+
+## ✅ Already Implemented (Core Features)
+
+- [x] **Basic bookmark management** - Add, edit, delete bookmarks with title, URL, and folder
+- [x] **Import/Export functionality** - Netscape HTML format with robust parsing and generation
+- [x] **Link testing** - Test all links, test invalid links only, with progress tracking
+- [x] **Search and filtering** - Real-time search with status-based filtering (all/valid/invalid/duplicate)
+- [x] **Duplicate detection** - URL normalization and duplicate marking
+- [x] **Data persistence** - localStorage with error handling
+- [x] **Folder organization** - Card-based layout grouped by folders
+- [x] **Context menu** - Right-click actions for individual bookmarks
+- [x] **Statistics display** - Real-time counts with clickable filter buttons
+- [x] **Basic responsive design** - Mobile breakpoints and layout adjustments
+- [x] **Progress indicators** - Progress bars for link testing operations
+- [x] **Basic error handling** - Try-catch blocks with user alerts for major operations
+
+## 🚀 Priority Tasks (High Impact)
+
+- [x] 1. Enhance folder selection in Add/Edit Bookmark dialog
+  - Implement HTML5 datalist for folder dropdown with existing folder options
+  - Add dynamic population of folder list from current bookmark collection
+  - Ensure both selection from dropdown and custom typing work seamlessly
+  - Update modal styling to accommodate the enhanced folder input
+  - _Requirements: 2.4, 2.5, 2.6_
+
+- [x] 2. Add keyboard navigation and accessibility features
+  - Implement tab order navigation through all interactive elements
+  - Add ARIA labels and semantic HTML structure for screen readers
+  - Enable Enter/Space key activation for buttons and bookmark items
+  - Add Escape key functionality to close modals
+  - Ensure high contrast ratios meet WCAG AA compliance
+  - _Requirements: 7.4, 7.5, 7.6, 7.7_
+
+- [x] 3. Optimize performance for large bookmark collections
+  - Implement debounced search with 300ms delay to reduce excessive filtering
+  - Add virtual scrolling or pagination for bookmark cards when collection exceeds threshold
+  - Optimize DOM manipulation to minimize reflows during rendering
+  - Add loading states for operations that might take time
+  - _Requirements: 10.1, 10.2, 10.3, 10.4, 10.5_
+
+## 🔧 Enhancement Tasks (Medium Priority)
+
+- [x] 4. Enhance link testing with better error categorization
+  - Improve error handling to categorize different types of link failures
+  - Add retry logic for transient network failures during testing
+  - Implement better timeout handling with user-configurable timeout values
+  - Add detailed error reporting in console for debugging failed links
+  - _Requirements: 3.3, 3.4, 3.6, 3.7_
+
+- [x] 5. Implement advanced duplicate detection algorithms
+  - Enhance URL normalization to handle more edge cases (query parameters, fragments)
+  - Add fuzzy matching for bookmark titles to detect near-duplicates
+  - Implement user choice for duplicate resolution (keep newest, oldest, or manual selection)
+  - Add preview of duplicates before marking them
+  - _Requirements: 5.2, 5.3, 5.4, 5.5_
+
+- [x] 6. Add data export options and backup features
+  - Implement multiple export formats (JSON, CSV, plain text)
+  - Add selective export by folder or status
+  - Create automatic backup reminders based on bookmark count or time
+  - Add import validation to prevent data corruption
+  - _Requirements: 1.6, 1.7, 1.8, 6.1_
+
+- [x] 7. Enhance mobile responsiveness and touch interactions
+  - Optimize touch targets for mobile devices (minimum 44px)
+  - Implement swipe gestures for bookmark actions on mobile
+  - Add pull-to-refresh functionality for link testing
+  - Optimize modal layouts for small screens
+  - _Requirements: 7.2, 7.3, 7.4_
+
+## 🎯 Advanced Features (Lower Priority)
+
+- [x] 8. Add advanced search and filtering capabilities
+  - Implement search within specific folders
+  - Add date-based filtering (added this week, month, year)
+  - Create saved search functionality
+  - Add search history and suggestions
+  - _Requirements: 4.1, 4.2, 4.3, 4.4_
+
+- [x] 9. Implement bookmark organization features
+  - Add drag-and-drop functionality to move bookmarks between folders
+  - Create folder management interface (rename, delete, merge folders)
+  - Add bulk operations (move multiple bookmarks, bulk delete)
+  - Implement bookmark sorting options (alphabetical, date, status)
+  - _Requirements: 2.1, 2.2, 2.7, 2.8_
+
+- [x] 10. Add bookmark metadata and tagging system
+  - Implement tagging system for bookmarks beyond folders
+  - Add bookmark notes/descriptions field
+  - Create bookmark rating or favorite system
+  - Add last visited tracking for bookmarks
+  - _Requirements: 1.3, 2.3, 9.1, 9.2_
+
+- [x] 11. Enhance statistics and reporting features
+  - Create detailed analytics dashboard showing bookmark usage patterns
+  - Add charts and graphs for bookmark statistics over time
+  - Implement bookmark health reports (broken links, old bookmarks)
+  - Add export functionality for statistics data
+  - _Requirements: 9.1, 9.2, 9.3, 9.4, 9.5, 9.6_
+
+- [x] 12. Implement advanced import/export features
+  - Add support for importing from multiple browser formats (Chrome, Firefox, Safari)
+  - Create incremental import to merge new bookmarks without duplicates
+  - Add import preview showing what will be imported before confirmation
+  - Implement bookmark synchronization between multiple devices
+  - _Requirements: 1.1, 1.2, 1.3, 1.4, 1.5_
+
+- [x] 13. Add bookmark sharing and collaboration features
+  - Create shareable bookmark collections with public URLs
+  - Add bookmark export to social media or email
+  - Implement bookmark recommendations based on similar collections
+  - Create bookmark collection templates for common use cases
+  - _Requirements: 1.6, 1.7, 1.8_
+
+- [x] 14. Implement advanced security and privacy features
+  - Add bookmark encryption for sensitive collections
+  - Implement secure bookmark sharing with password protection
+  - Add privacy mode to exclude certain bookmarks from exports
+  - Create bookmark access logging for security auditing
+  - _Requirements: 6.1, 6.2, 6.3, 6.4_