feat: major project restructure - move Django to backend dir and fix critical imports

- Restructure project: moved Django backend to backend/ directory
- Add frontend/ directory for future Next.js application
- Add shared/ directory for common resources
- Fix critical Django import errors:
  - Add missing sys.path modification for apps directory
  - Fix undefined CATEGORY_CHOICES imports in rides module
  - Fix media migration undefined references
  - Remove unused imports and f-strings without placeholders
- Install missing django-environ dependency
- Django server now runs without ModuleNotFoundError
- Update .gitignore and README for new structure
- Add pnpm workspace configuration for monorepo setup

static/js/alerts.js

@@ -1,18 +0,0 @@
-document.addEventListener('DOMContentLoaded', function() {
-    // Get all alert elements
-    const alerts = document.querySelectorAll('.alert');
-    
-    // For each alert
-    alerts.forEach(alert => {
-        // After 5 seconds
-        setTimeout(() => {
-            // Add slideOut animation
-            alert.style.animation = 'slideOut 0.5s ease-out forwards';
-            
-            // Remove the alert after animation completes
-            setTimeout(() => {
-                alert.remove();
-            }, 500);
-        }, 5000);
-    });
-});