✨ Add comprehensive admin panel with user management

Features added:
- Admin authentication system with is_admin field
- Complete admin dashboard with user statistics
- User management (create, edit, delete, toggle admin)
- Protected admin routes with @admin_required decorator
- Security features (prevent self-deletion, last admin protection)
- Responsive admin UI with Bootstrap integration
- Database migration script for admin field
- Admin navigation link for authorized users

Technical improvements:
- Enhanced 3-column dashboard layout (tables | editor | saved queries)
- Removed plus button and made right sidebar more compact
- Admin user (admin/admin123) automatically created with admin privileges
- Full CRUD operations for user management
- Flash messages for user feedback
- Form validation and error handling

.gitignore

@@ -0,0 +1,63 @@
+# Python
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# Flask
+instance/
+.webassets-cache
+
+# Environment variables
+.env
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# OS
+.DS_Store
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+ehthumbs.db
+Thumbs.db
+
+# Database
+*.db
+*.sqlite
+*.sqlite3
+
+# Logs
+*.log
+
+# Virtual Environment
+.venv/
+venv/
+ENV/
+env/
+.env
+
+# Temporary files
+*.tmp
+*.temp