Restructure project for security and offline capability

- Move content outside public web root for security
- Consolidate all code and assets in engine/ directory
- Download Bootstrap locally for offline functionality
- Update public/ to contain only entry point files
- Add router.php for PHP development server security
- Update README.md with new structure and setup instructions
- Block direct access to content files via URL
- Maintain clean separation between content and code

public/.htaccess

@@ -44,10 +44,8 @@
     RewriteCond %{REQUEST_FILENAME} -f
     RewriteRule ^assets/.*$ - [L]
     
-    # Allow access to content files (except PHP)
-    RewriteCond %{REQUEST_FILENAME} -f
-    RewriteCond %{REQUEST_FILENAME} !\.php$
-    RewriteRule ^content/.*$ - [L]
+    # Block direct access to all content files
+    RewriteRule ^content/.*$ - [F,L]
 </IfModule>
 
 # Security headers