[Studio] Use Consumer Group APIs when mock mode is disabled.

[Kris20030907]

What is the purpose of the change

• [Studio] Use Consumer Group APIs when mock mode is disabled #647

Problem

The Consumer Group page directly uses mock data and bypasses the existing service layer. As a result, the page still displays mock groups when mock mode is disabled, and create, delete, and reset actions can report success without updating the backend.

Expected behavior

• Load consumer groups, subscriptions, and progress through the service layer.
• Send create, delete, batch delete, and reset-offset operations to the backend.
• Update the page and show success only after the request succeeds.
• Keep the current state and show an error when the request fails.

Proposed fix

Connect the Consumer Group page to the existing consumer service APIs, add loading and error handling, and cover the main flows with page-level regression tests.