test: migrate remaining resource commands and remove legacy mock-command coverage

[guoqqqi]

Refs #19

Goal

Complete the migration after the first core-resource batch by moving the remaining command behavior coverage to real APISIX E2E and cleaning up the old mocked-command test inventory.

Remaining Areas

• consumer / credential / consumer-group
• ssl / stream-route / proto / secret / plugin-metadata
• debug / completion / version / extension / context where applicable
• any remaining pkg/cmd/** tests whose primary value depends on mocked Admin API responses

Scope

• finish the remaining resource-family migrations in batches
• keep only self-contained unit tests for pure logic
• remove stale httpmock-based command tests once E2E equivalents exist
• update CI and test inventory docs as the migration completes

Acceptance Criteria

• command behavior coverage is centered on real APISIX E2E across the repository
• only pure-logic unit tests remain outside E2E for command-adjacent helpers
• old mocked Admin API command tests are removed from normal maintenance paths
• repository docs and CI reflect the new steady-state testing strategy