refact: openapi splitted into separate files

api/schemas/User.yaml

@@ -0,0 +1,40 @@
+type: object
+properties:
+  id:
+    type: integer
+    format: int64
+    description: Unique user ID (primary key)
+    example: 1
+  avatar_id:
+    type: integer
+    format: int64
+    description: ID of the user avatar (references images table)
+    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