test: migrate core command coverage from mocked Admin API tests to real E2E

[guoqqqi]

Refs #19

Goal

Migrate the first high-value batch of command coverage away from mocked Admin API tests and into real APISIX E2E scenarios.

First Batch

• route
• service
• upstream
• plugin-config
• global-rule / label / export combinations

Scope

• add or migrate real E2E coverage for CRUD and key integration paths
• cover at least one real gateway traffic validation path per core resource family
• delete or retire the corresponding mocked command tests once equivalent E2E coverage is in place
• keep pure helper/unit tests only where external mocking is not needed

Acceptance Criteria

• core command behavior is no longer primarily verified through mocked Admin API responses
• corresponding Ginkgo E2E scenarios exist for CRUD and resource-combination flows
• legacy mocked command tests for the migrated batch are removed or clearly retired
• CI remains green and stable after the migration