fix(tests): align CI tests with A2A boundary refactor

The shared `format_data` serializer introduced for the CLI→Application
A2A boundary returns raw payloads without the `{"data": ...}` envelope
that the legacy CLI `format_output` wraps around. Two test-step
definitions (`step_artifacts_json_validation`,
`step_artifacts_json_apply_summary`) still unwrapped that envelope and
crashed with `KeyError: 'data'`, errrring the Behave scenarios
`Plan artifacts shows validation results when available` and
`Artifacts include apply summary from metadata`.

Also remove the stale `@tdd_expected_fail` tag from the Robot scenario
`WF02 Mocked Generation Produces Test Artifacts Only`: the scenario
exercises the `_cleveragents/plan/artifacts` A2A dispatch path that this
PR added and now passes naturally; the `tdd_expected_fail_listener`
inverts the passing result to a failure with "Bug appears to be fixed.
Remove the tdd_expected_fail tag".

Adds a CHANGELOG entry covering both the boundary refactor and these
test alignments.

Refs: #9962
Refs: #4253

robot/wf02_test_generation_integration.robot

@@ -28,7 +28,7 @@ WF02 Mocked Generation Produces Test Artifacts Only
     [Documentation]    Verify mocked LLM responses generate deterministic test
     ...                files, assert user-facing plan artifacts command path,
     ...                and artifacts list only test paths (no prod edits).
-    [Tags]    tdd_issue    tdd_issue_4296    tdd_expected_fail    mocking    artifacts    invariants
+    [Tags]    tdd_issue    tdd_issue_4296    mocking    artifacts    invariants
     ${result}=    Run Process    ${PYTHON}    ${HELPER}    mocked-generation-artifacts    cwd=${WORKSPACE}    timeout=120s    on_timeout=kill
     Log    ${result.stdout}
     Log    ${result.stderr}