feat(faq): support rich-text image upload and RAG output

- add FAQ image upload API with MinIO path and mime/size validation

- enable FAQ editor image upload and text-or-image validation

- include FAQ image metadata in vector content and retrieval output

- enforce markdown image preservation via bot system prompt rule

easyflow-ui-admin/app/src/locales/langs/zh-CN/documentCollection.json

@@ -108,7 +108,11 @@
     "questionPlaceholder": "请输入问题",
     "answerPlaceholder": "请输入答案",
     "questionRequired": "问题不能为空",
-    "answerRequired": "答案不能为空"
+    "answerRequired": "答案不能为空",
+    "collectionRequired": "知识库ID不能为空",
+    "imageTypeInvalid": "仅支持 JPG/PNG/WEBP/GIF 图片",
+    "imageSizeExceeded": "图片大小不能超过5MB",
+    "imageUploadFailed": "图片上传失败"
   },
   "searchResults": "检索结果",
   "documentPreview": "文档预览",