feat: complete codebase refactor with Flask best practices

- Implement application factory pattern with blueprints
- Add modular structure (models, routes, utils, templates)
- Create configuration management system
- Add comprehensive error handling and logging
- Implement cookie-based like system with database migration
- Add proper authentication decorators and session management
- Update .gitignore to exclude database files and OS artifacts

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

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

.gitignore

@@ -8,3 +8,16 @@ wheels/
 
 # Virtual environments
 .venv
+
+# Database files
+*.db
+pet_pictures.db
+
+# OS generated files
+.DS_Store
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+ehthumbs.db
+Thumbs.db