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/assets/favicon.svg

@@ -1,11 +0,0 @@
-<svg width="32" height="32" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg">
-  <!-- < -->
-  <path d="M8 8 L3 16 L8 24" stroke="#ffffff" stroke-width="3" fill="none" stroke-linecap="round" stroke-linejoin="round"/>
-  
-  <!-- / -->
-  <path d="M12 24 L18 8" stroke="#ffffff" stroke-width="3" stroke-linecap="round"/>
-  
-  <!-- .. -->
-  <circle cx="22" cy="20" r="2" fill="#ffffff"/>
-  <circle cx="28" cy="20" r="2" fill="#ffffff"/>
-</svg>

public/assets/icon.svg

@@ -1,11 +0,0 @@
-<svg width="32" height="32" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg">
-  <!-- < -->
-  <path d="M8 8 L3 16 L8 24" stroke="#ffffff" stroke-width="3" fill="none" stroke-linecap="round" stroke-linejoin="round"/>
-  
-  <!-- / -->
-  <path d="M12 24 L18 8" stroke="#ffffff" stroke-width="3" stroke-linecap="round"/>
-  
-  <!-- .. -->
-  <circle cx="22" cy="20" r="2" fill="#ffffff"/>
-  <circle cx="28" cy="20" r="2" fill="#ffffff"/>
-</svg>