feat: isolate profanity filter with separate database

- Create dedicated ProfanityFilter class with isolated SQLite database
- Separate profanity.db from main application database to prevent SQLITE_MISUSE errors
- Add comprehensive custom word management (CRUD operations)
- Implement advanced profanity detection with leetspeak and pattern matching
- Add admin UI for managing custom profanity words
- Add extensive test suites for both profanity filter and API routes
- Update server.js to use isolated profanity filter
- Add proper database initialization and cleanup methods
- Support in-memory databases for testing

Breaking changes:
- Profanity filter now uses separate database file
- Updated admin API endpoints for profanity management
- Enhanced profanity detection capabilities

public/admin.html

@@ -319,7 +319,10 @@
     <div class="admin-container">
         <!-- Login Section -->
         <div id="login-section" class="login-section">
-            <h2>🔐 Admin Login</h2>
+            <div style="display: flex; justify-content: space-between; align-items: center; margin-bottom: 20px;">
+                <h2 style="margin: 0;">🔐 Admin Login</h2>
+                <a href="/" class="header-btn btn-home" style="text-decoration: none; font-size: 12px; padding: 8px 12px;">🏠 Back to Homepage</a>
+            </div>
             <form id="login-form">
                 <div class="form-group">
                     <label for="password">Admin Password:</label>
@@ -387,6 +390,6 @@
         </div>
     </div>
 
-    <script src="https://iceymi.b-cdn.net/admin.js"></script>
+    <script src="admin.js"></script>
 </body>
 </html>