feat: Implement live reasoning streaming with timing display

- Update ReasoningBlock to start expanded and show live reasoning content
- Add timing tracking with start/end timestamps for reasoning duration
- Auto-collapse reasoning blocks after completion with 500ms delay
- Show timing summary (e.g. 'Thought for 0.4s') instead of content when collapsed
- Add streaming cursor animation and real-time content updates
- Update types to support reasoning timing and streaming state
- Stream reasoning content live as tokens arrive during thinking phase

This provides a much better UX where users can see the model thinking
in real-time, then get a clean timing summary after completion.

examples/chat-ui/src/components/ChatMessage.tsx

@@ -39,8 +39,13 @@ const ChatMessage: React.FC<ChatMessageProps> = ({
         }`}
       >
         {/* Show reasoning block for assistant messages with reasoning */}
-        {message.role === "assistant" && "reasoning" in message && message.reasoning && (
-          <ReasoningBlock reasoning={message.reasoning} />
+        {message.role === "assistant" && "reasoning" in message && (message.reasoning || message.isReasoningStreaming) && (
+          <ReasoningBlock 
+            reasoning={message.reasoning || ""} 
+            isStreaming={message.isReasoningStreaming}
+            startTime={message.reasoningStartTime}
+            endTime={message.reasoningEndTime}
+          />
         )}
         
         <div className="prose prose-zinc">