fnos: 修复飞牛链接失效

fixes #555
fixes #557

reinstall.sh

@@ -1654,25 +1654,18 @@ Continue with DD?
             fi
         done
 
-        if [ "$basearch" = aarch64 ]; then
-            if [ -z "$iso" ]; then
-                IFS= read -r -p "ISO Link: " iso
-                if [ -z "$iso" ]; then
-                    error_and_exit "ISO Link is empty."
-                fi
-            fi
-        else
-            iso=$(curl -L https://fnnas.com/ | grep -o -m1 'https://[^"]*\.iso')
+        # 对于同一行有多个成功匹配，grep -m1 无效
+        iso=$(curl -L "https://fnnas.com/download$([ "$basearch" = aarch64 ] && echo -arm)" |
+            grep -o 'https://[^"]*\.iso' | head -1 | grep .)
 
-            # curl 7.82.0+
-            # curl -L --json '{"url":"'$iso'"}' https://www.fnnas.com/api/download-sign
+        # curl 7.82.0+
+        # curl -L --json '{"url":"'$iso'"}' https://www.fnnas.com/api/download-sign
 
-            iso=$(curl -L \
-                -d '{"url":"'$iso'"}' \
-                -H 'Content-Type: application/json' \
-                https://www.fnnas.com/api/download-sign |
-                grep -o 'https://[^"]*')
-        fi
+        iso=$(curl -L \
+            -d '{"url":"'$iso'"}' \
+            -H 'Content-Type: application/json' \
+            https://www.fnnas.com/api/download-sign |
+            grep -o 'https://[^"]*')
 
         test_url "$iso" iso
         eval "${step}_iso='$iso'"