feat: add streaming responses with optional toggle

- Add server-sent events (SSE) streaming support for real-time token display
- Implement progressive markdown rendering during streaming
- Add stream toggle in API settings (defaults to disabled for compatibility)
- Add visual streaming indicator with pulsing animation
- Graceful fallback to non-streaming mode when disabled
- Fix character saving bug (camelCase parameter naming)

Backend changes:
- New chat_stream command with SSE parsing
- Added futures and bytes dependencies
- Emit chat-token events progressively to frontend
- Support for OpenAI-compatible and Anthropic streaming formats

Frontend changes:
- Dual code paths for streaming/non-streaming
- Real-time markdown and syntax highlighting during streaming
- Stream status indicator with animation

src/index.html

@@ -104,6 +104,13 @@
               </select>
             </div>
 
+            <div class="form-group">
+              <label>
+                <input type="checkbox" id="stream-toggle" />
+                Enable streaming responses (real-time token display)
+              </label>
+            </div>
+
             <div id="validation-message" class="validation-message"></div>
 
             <button type="submit" id="save-settings-btn" class="btn-primary" disabled>