mplement proper async initialization for ProfanityFilter

- Add async initialize() method for reliable initialization waiting
- Add static create() factory method for easy async creation
- Add initialization state tracking with isInitialized flag
- Add warning system for methods called before full initialization
- Update server.js to use proper async initialization pattern
- Maintain backward compatibility with constructor-only usage
- Add accessibility improvement for reduced motion preferences in CSS

Fixes the race condition issue where consumers relied on arbitrary
timeouts instead of properly waiting for async initialization to complete.

public/style.css

@@ -219,7 +219,13 @@ button[type="submit"]:hover {
     color: #721c24;
     border: 2px solid #dc3545;
     font-weight: bold;
-    animation: pulse 0.5s ease-in-out;
+}
+
+/* Only animate for users who haven't requested reduced motion */
+@media (prefers-reduced-motion: no-preference) {
+    .message.error.profanity-rejection {
+        animation: pulse 0.5s ease-in-out;
+    }
 }
 
 [data-theme="dark"] .message.error.profanity-rejection {