Add reference design images, point task.json at relative paths

tasks/c26/task.json

@@ -16,7 +16,7 @@
  ],
  "domain": "电商",
  "seed_meta": {
-  "ref_image_src": null
+  "ref_image_src": "prototypes/reference.jpg"
  },
  "title": "PaulHoda.UK SEO 站点复刻 + 方案商城与结算流程",
  "milestones": [