feat: enhance superadmin dashboard overview

backend/docs/swagger.yaml

@@ -1048,6 +1048,17 @@ definitions:
     required:
     - action
     type: object
+  dto.SuperContentStatisticsResponse:
+    properties:
+      total_count:
+        description: TotalCount 内容总量。
+        type: integer
+      trend:
+        description: Trend 按天新增内容趋势。
+        items:
+          $ref: '#/definitions/dto.SuperContentTrendItem'
+        type: array
+    type: object
   dto.SuperContentTenantLite:
     properties:
       code:
@@ -1060,6 +1071,15 @@ definitions:
         description: Name 租户名称。
         type: string
     type: object
+  dto.SuperContentTrendItem:
+    properties:
+      created_count:
+        description: CreatedCount 当日新增内容数量。
+        type: integer
+      date:
+        description: Date 日期（YYYY-MM-DD）。
+        type: string
+    type: object
   dto.SuperCouponGrantItem:
     properties:
       coupon_id:
@@ -2500,6 +2520,21 @@ paths:
       summary: Batch review contents
       tags:
       - Content
+  /super/v1/contents/statistics:
+    get:
+      consumes:
+      - application/json
+      description: Content statistics
+      produces:
+      - application/json
+      responses:
+        "200":
+          description: OK
+          schema:
+            $ref: '#/definitions/dto.SuperContentStatisticsResponse'
+      summary: Content statistics
+      tags:
+      - Content
   /super/v1/coupon-grants:
     get:
       consumes: