feat(content): 资讯富编辑(封面/图集/视频/外链/发布人) + 媒体上传

- 迁移0016：content_items 加 cover/images_json/video/video_cover/link/publisher_name/publisher_avatar
- ContentRepository：_to_dict/create/update 支持富字段；images(list)↔images_json；update 白名单含 publisher_id
- schemas：ContentCreate/UpdateRequest 加富字段
- rbac_operator：POST /content 注入发布人(actor 昵称/头像快照)；新增 POST /admin/upload(媒体上传)
- app/services/media_upload.py：统一上传(serverdata/uploads + abs_url)，与 /api/upload 同契约

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

app/api/schemas/operator.py

@@ -86,10 +86,16 @@ class ContentCreateRequest(BaseModel):
     title: str
     summary: str = ""
     body: str = ""
+    cover: str = ""                 # 封面图
+    images: list[str] = []          # 图集
+    video: str = ""                 # 视频 URL
+    video_cover: str = ""           # 视频封面
+    link: str = ""                  # 外链
+    publisher_name: str = ""        # 发布人昵称（空则用操作者）
+    publisher_avatar: str = ""      # 发布人头像
     status: str = "draft"
 
 
-
 class ContentStatusRequest(BaseModel):
     status: str  # published/offline/draft
 
@@ -100,6 +106,13 @@ class ContentUpdateRequest(BaseModel):
     title: str | None = None
     summary: str | None = None
     body: str | None = None
+    cover: str | None = None
+    images: list[str] | None = None
+    video: str | None = None
+    video_cover: str | None = None
+    link: str | None = None
+    publisher_name: str | None = None
+    publisher_avatar: str | None = None
     status: str | None = None