fix: enable UI retry when Bedrock returns early 503 error (#94)

- Add error prop to ChatInput to detect error state
- Update isDisabled logic to allow retry when there's an error
- Pass combined error (SDK error + streamingError) to ChatInput

When Bedrock returns 503 ServiceUnavailableException before streaming
starts, AI SDK's onError fires but status may not transition to "ready".
This fix ensures the input is re-enabled when an error occurs, allowing
users to retry their request.

components/chat-panel.tsx

@@ -164,7 +164,7 @@ Please retry with an adjusted search pattern or use display_diagram if retries a
     const lastMessagePartsRef = useRef(0);
 
     useEffect(() => {
-        // Clear streaming error and reset refs when status changes to ready
+        // Clear streaming error when status changes to ready
         if (status === "ready") {
             setStreamingError(null);
             lastMessageCountRef.current = 0;
@@ -498,6 +498,7 @@ Please retry with an adjusted search pattern or use display_diagram if retries a
                     onFileChange={handleFileChange}
                     showHistory={showHistory}
                     onToggleHistory={setShowHistory}
+                    error={error || streamingError}
                 />
             </footer>
         </div>