fix: Fix failing integration tests and update documentation

- Fix TestUpdateDevice: Use correct JSON field name and handle float64 type
- Fix TestRejectDeviceRegistration: Expect message response instead of boolean
- Update approve device docs: Add missing response fields
- Update reject device docs: Correct message text and format
- Update Bruno API: Fix example response for reject endpoint

Both integration tests now pass while maintaining API consistency.

bruno/devices/Reject Device Registration.bru

@@ -33,11 +33,10 @@ docs {
    - 404: Registration not found
    - 400: Invalid registration status
 
-  **Example Response:**
-   ```json
-   {
-     "message": "Device registration rejected",
-     "registration_id": "uuid"
-   }
-   ```
+   **Example Response:**
+    ```json
+    {
+      "message": "device registration rejected"
+    }
+    ```
 }