Update PassthroughGeminiResponseStream to handle [DONE] marker

- Added logic to return an empty slice when the raw JSON equals the `[DONE]` marker.
- Ensures proper termination of streamed Gemini responses.

internal/translator/gemini/gemini/gemini_gemini_response.go

@@ -1,11 +1,15 @@
 package gemini
 
 import (
+	"bytes"
 	"context"
 )
 
 // PassthroughGeminiResponseStream forwards Gemini responses unchanged.
 func PassthroughGeminiResponseStream(_ context.Context, _ string, rawJSON []byte, _ *any) []string {
+	if bytes.Equal(rawJSON, []byte("[DONE]")) {
+		return []string{}
+	}
 	return []string{string(rawJSON)}
 }