Bootstrap copied BFF and local accounts with public Sendico contracts (#34)

backend/contracts/sendico/models/auth/login_data.yaml

@@ -0,0 +1,21 @@
+components:
+  schemas:
+    LoginData:
+      description: Credentials and optional locale used during user sign-in.
+      type: object
+      additionalProperties: false
+      required:
+        - login
+        - password
+      properties:
+        login:
+          description: User login identifier, represented as an email address.
+          type: string
+          format: email
+        password:
+          description: User password submitted for authentication.
+          type: string
+          format: password
+        locale:
+          description: Optional locale preference provided at login time.
+          type: string