feat: add User scahema to api

api/openapi.yaml

@@ -540,7 +540,47 @@ components:
       additionalProperties: true
     User:
       type: object
-      additionalProperties: true
+      properties:
+        user_id:
+          type: integer
+          format: int32
+          description: Unique user ID (primary key)
+          example: 1
+        avatar_id:
+          type: integer
+          format: int32
+          description: ID of the user avatar (references images table)
+          nullable: true
+          example: null
+        mail:
+          type: string
+          format: email
+          description: User email
+          example: "john.doe@example.com"
+        nickname:
+          type: string
+          description: Username (alphanumeric + _ or -)
+          maxLength: 16
+          example: "john_doe_42"
+        disp_name:
+          type: string
+          description: Display name
+          maxLength: 32
+          example: "John Doe"
+        user_desc:
+          type: string
+          description: User description
+          maxLength: 512
+          example: "Just a regular user."
+        creation_date:
+          type: string
+          format: date-time
+          description: Timestamp when the user was created
+          example: "2025-10-10T23:45:47.908073Z"
+      required:
+        - user_id
+        - nickname
+        - creation_date
     UserTitle:
       type: object
       additionalProperties: true