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/en-US/documentCollection.json

@@ -108,7 +108,11 @@
     "questionPlaceholder": "Please input question",
     "answerPlaceholder": "Please input answer",
     "questionRequired": "Question is required",
-    "answerRequired": "Answer is required"
+    "answerRequired": "Answer is required",
+    "collectionRequired": "Collection id is required",
+    "imageTypeInvalid": "Only JPG/PNG/WEBP/GIF images are supported",
+    "imageSizeExceeded": "Image size must be less than 5MB",
+    "imageUploadFailed": "Image upload failed"
   },
   "searchResults": "SearchResults",
   "documentPreview": "DocumentPreview",