Land docs/ga-test-plan.md and achieve automated E2E parity with the manual pass

[shreemaan-abhishek]

Land docs/ga-test-plan.md modelled on a7's plan. Ensure every scenario walked manually in the smoke validation sub-issue has a corresponding Ginkgo test in test/e2e/, staying within #14's 2026-04-28 boundary: CLI -> real Admin API -> CLI read-back, not real proxy traffic. Where the manual pass exposed an automated gap, add the test.

Part of #33

[shreemaan-abhishek]

only formatting related cases are not covered