Move TTS server status from frontend to admin dashboard

- Removed TTS server status popup from main frontend interface
- Commented out checkTtsServer() function and all its calls
- Removed TTS configuration UI elements from index.html
- Added comprehensive TTS server monitoring to admin dashboard:
  - Configuration status (URL, API key)
  - Server health monitoring
  - Available voices display
  - Usage statistics and performance metrics
  - Real-time status updates
- Enhanced system health check to include TTS server
- Created dedicated /api/tts/status endpoint for detailed info

The TTS functionality remains fully operational for users, but status
monitoring is now exclusive to the admin dashboard for cleaner UX.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

templates/index.html

@@ -354,7 +354,8 @@
 
         <audio id="audioPlayer" style="display: none;"></audio>
         
-        <!-- TTS Server Configuration Alert -->
+        <!-- TTS Server Configuration Alert - Moved to Admin Dashboard -->
+        <!-- Commenting out user-facing TTS server configuration
         <div id="ttsServerAlert" class="alert alert-warning d-none" role="alert">
             <strong>TTS Server Status:</strong> <span id="ttsServerMessage">Checking...</span>
             <div class="mt-2">
@@ -363,6 +364,7 @@
                 <button id="updateTtsServer" class="btn btn-sm btn-primary">Update Configuration</button>
             </div>
         </div>
+        -->
         
         <!-- Loading Overlay -->
         <div id="loadingOverlay" class="loading-overlay">