fix: preserve newlines in SSE streaming for Markdown rendering

internal/web/server.go

@@ -41,12 +41,16 @@ func (w *sseWriter) Write(p []byte) (n int, err error) {
 	default:
 	}
 
-	data := strings.ReplaceAll(string(p), "\n", "")
-	if data == "" {
+	data := string(p)
+	if strings.TrimSpace(data) == "" {
 		return len(p), nil
 	}
 
-	fmt.Fprintf(w.client.Writer, "data: %s\n\n", data)
+	lines := strings.Split(data, "\n")
+	for _, line := range lines {
+		fmt.Fprintf(w.client.Writer, "data: %s\n", line)
+	}
+	fmt.Fprint(w.client.Writer, "\n")
 	w.client.Flusher.Flush()
 	return len(p), nil
 }