feat(admin): media library + upload component (replace URL fields)

- /admin/files Media Library: drag-drop multi-upload, thumbnails, copy-URL, delete
- FileUploadField replaces raw URL inputs; new "image" field type in AdminResource;
  wired into category image
- upload proxy /api/admin/files/upload: browser → Next → presigned PUT (server-side,
  reaches minio:9000) → confirm → returns public URL
- user-uploads bucket is public-read; public base via NEXT_PUBLIC_MINIO_URL

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

messages/en.json

@@ -320,7 +320,8 @@
       "slides": "Slides",
       "users": "Users",
       "plans": "Plans",
-      "templates": "Templates"
+      "templates": "Templates",
+      "media": "Media"
     },
     "appAdminNodesPage": {
       "title": "Render Nodes",

messages/fa.json

@@ -320,7 +320,8 @@
       "slides": "اسلایدها",
       "users": "کاربران",
       "plans": "پلن‌ها",
-      "templates": "قالب‌ها"
+      "templates": "قالب‌ها",
+      "media": "رسانه"
     },
     "appAdminNodesPage": {
       "title": "نودهای رندر",