docs: Add comprehensive CHANGELOG.md

Complete changelog with all versions from 1.3.7 to 1.5.4:
- Detailed feature descriptions and improvements
- Technical implementation notes
- Docker image information and migration notes
- Support and contribution guidelines

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

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

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [1.5.4] - 2025-09-09
+
+### Added
+- **Visual clear form tip**: Added visible tip in interface showing correct keyboard shortcut
+  - Automatically detects Mac vs Windows/Linux operating system
+  - Shows 'Cmd + Shift + R' on Mac systems
+  - Shows 'Ctrl + Shift + R' on Windows/Linux systems
+  - Clean, non-intrusive design with blue accent border
+  - Positioned below 'Generar Venta' button for easy visibility
+
+### Technical
+- JavaScript OS detection using `navigator.platform`
+- Dynamic content update based on detected operating system
+- CSS styling for `.clear-form-tip` class with responsive design
+- Updated cache-busting version for immediate loading
+
+## [1.5.3] - 2025-09-08
+
+### Fixed
+- **Date formatting bug**: Resolved critical bug showing "undefined" in ticket receipts
+- **esc() function**: Fixed regex pattern that was corrupting date slashes
+- **Date validation**: Improved robust date handling throughout the system
+
+### Improved
+- **Ticket layout**: All ticket content now left-aligned for better readability
+- **Interface compactness**: Reduced product card spacing for less scrolling
+- **Auto-collapse**: Product categories automatically collapse after adding items
+- **User experience**: Streamlined workflow and cleaner interface
+
+### Removed
+- **Clear form button**: Removed problematic clear button per user feedback
+
+### Added
+- **Favicon integration**: Complete favicon support across all pages
+  - Apple Touch Icon (180x180) for iOS devices
+  - Standard favicons (16x16, 32x32) for browsers
+  - High-resolution icons (192x192, 512x512) for PWA support
+  - Web manifest for progressive web app installation
+  - Professional branding across all device types
+
+## [1.5.0] - 2025-09-07
+
+### Added
+- **Dashboard reorganization**: New sub-tab structure in sales section
+  - "💰 Ventas" sub-tab for active sales operations
+  - "🎫 Tickets" sub-tab for sales history and reports
+- **Advanced anticipos system**: 
+  - Manual anticipo application for unregistered payments
+  - Security checkbox confirmation for manual anticipos
+  - Automatic integration with discount system
+  - Duplication prevention controls
+
+### Improved
+- **Client management**: 
+  - "Público General" automatic system for anonymous sales
+  - Optional client field (no longer mandatory)
+  - Generic ticket support for walk-in customers
+- **Visual enhancements**:
+  - Solid black header replacing gradient design
+  - Improved price alignment with grid layout
+  - Consistent color scheme and styling
+  - Logical service ordering: Clean Girl → Elegant → Mystery → Seduction
+
+### Technical
+- Enhanced database schema with `sort_order` field
+- Functional sub-tab navigation with JavaScript
+- Reinforced form validation and data controls
+- Performance optimizations and code refactoring
+
+## [1.4.1] - 2025-09-06
+
+### Fixed
+- Production environment issues in VPS deployment
+- Database connection stability improvements
+- Error handling enhancements
+
+## [1.4.0] - 2025-09-05
+
+### Added
+- Product import functionality with CSV support
+- Multiple payment method options
+- Enhanced checkout flow
+
+### Improved
+- User interface consistency
+- Form validation and error handling
+
+## [1.3.7] - 2025-09-04
+
+### Fixed
+- Critical bug fixes in payment processing
+- Database integrity improvements
+- UI responsiveness issues
+
+### Enhanced
+- Security improvements
+- Performance optimizations
+
+---
+
+## Docker Images
+
+All versions are available on Docker Hub:
+
+```bash
+# Latest stable version
+docker pull marcogll/ap-pos:latest
+
+# Specific version
+docker pull marcogll/ap-pos:1.5.4
+```
+
+### Version Tags Available:
+- `latest` - Always points to the most recent stable release
+- `1.5.4` - Visual clear form tip with OS detection
+- `1.5.3` - Date fixes and favicon integration  
+- `1.5.2` - Interface improvements
+- `1.5.1` - Bug fixes and optimizations
+- `1.5.0` - Major UI overhaul and anticipos system
+- `1.4.1` - Production stability fixes
+- `1.4.0` - Product import and payment methods
+- `1.3.7` - Core functionality and bug fixes
+
+## Migration Notes
+
+### From 1.5.x to 1.5.4
+- No database changes required
+- New visual tip will appear automatically
+- OS detection works immediately on page load
+
+### From 1.4.x to 1.5.x
+- Database will auto-upgrade with new fields
+- Existing data remains intact
+- New sub-tab structure provides better organization
+
+### From 1.3.x to 1.4.x
+- Backup recommended before upgrade
+- New payment methods will be available
+- Enhanced product management features
+
+## Support
+
+For issues, feature requests, or contributions, please visit the project repository or contact the development team.