2026-05-28 prompt-template audit: align to authoritative source

metadata.json

@@ -10,7 +10,7 @@
         "single_image_start"
       ],
       "task_type": "captioning",
-      "prompt_template": "<image>{{ question }}",
+      "prompt_template": "<image>Provide a one-sentence caption for the provided image.",
       "mapping_from_source": {
         "media": {
           "from": "image",