fix(cli): add <REGEX> positional argument to agents plan list command

The <REGEX> positional argument was already implemented in the CLI code
(src/cleveragents/cli/commands/plan.py) in a prior commit. This commit
adds the missing Robot Framework integration test that verifies the
argument is accepted and correctly filters plan names by regex pattern.

Changes:
- robot/helper_plan_cli_spec.py: Add list_regex() helper function that
  creates two mock plans (local/smoke-plan and local/other-plan), invokes
  'agents plan list --format json smoke.*', and verifies that only the
  matching plan appears in the output.
- robot/plan_cli_spec.robot: Add 'Plan Lifecycle List Accepts Regex
  Positional Argument' test case that calls the list-regex helper and
  asserts the plan-cli-list-regex-ok sentinel is printed.

The Behave unit test scenario ('Plan list with regex filter') already
existed in features/plan_cli_spec_alignment.feature and the step
definition in features/steps/plan_cli_spec_alignment_steps.py.

Closes #3436

robot/helper_plan_cli_spec.py

@@ -269,6 +269,57 @@ def list_columns() -> None:
         print("plan-cli-list-columns-ok")
 
 
+def list_regex() -> None:
+    """Verify list accepts a positional <REGEX> argument and filters by name."""
+    mock_service = MagicMock()
+    matching_plan = _mock_plan()  # name: local/smoke-plan, action: local/smoke-action
+    now = matching_plan.timestamps.created_at
+    non_matching_plan = Plan(
+        identity=PlanIdentity(plan_id="01KHDE6WWS2171PWW3GJEBXZ8S"),
+        namespaced_name=NamespacedName.parse("local/other-plan"),
+        description="Other plan",
+        definition_of_done="Done",
+        action_name="local/other-action",
+        phase=PlanPhase.STRATEGIZE,
+        processing_state=ProcessingState.QUEUED,
+        project_links=[],
+        arguments={},
+        arguments_order=[],
+        automation_profile=AutomationProfileRef(
+            profile_name="trusted",
+            provenance=AutomationProfileProvenance.PLAN,
+        ),
+        estimation_actor="openai/gpt-4",
+        invariant_actor="openai/gpt-4",
+        strategy_actor="openai/gpt-4",
+        execution_actor="openai/gpt-4",
+        reusable=True,
+        read_only=False,
+        created_by=None,
+        timestamps=PlanTimestamps(created_at=now, updated_at=now),
+    )
+    mock_service.list_plans.return_value = [matching_plan, non_matching_plan]
+    with patch(
+        "cleveragents.cli.commands.plan._get_lifecycle_service",
+        return_value=mock_service,
+    ):
+        # Use JSON format so full names are visible (rich table truncates them)
+        result = runner.invoke(plan_app, ["list", "--format", "json", "smoke.*"])
+        if result.exit_code != 0:
+            print(f"FAIL: list regex returned {result.exit_code}", file=sys.stderr)
+            print(result.output, file=sys.stderr)
+            sys.exit(1)
+        if "smoke-plan" not in result.output:
+            print("FAIL: matching plan not in output", file=sys.stderr)
+            print(result.output, file=sys.stderr)
+            sys.exit(1)
+        if "other-plan" in result.output:
+            print("FAIL: non-matching plan appeared in output", file=sys.stderr)
+            print(result.output, file=sys.stderr)
+            sys.exit(1)
+        print("plan-cli-list-regex-ok")
+
+
 def status_fields() -> None:
     """Verify plan status renders required fields."""
     mock_service = MagicMock()
@@ -329,6 +380,7 @@ _COMMANDS = {
     "use-actor-overrides": use_actor_overrides,
     "list-filters": list_filters,
     "list-columns": list_columns,
+    "list-regex": list_regex,
     "status-fields": status_fields,
     "cancel-reason": cancel_reason,
 }

robot/plan_cli_spec.robot

@@ -40,6 +40,14 @@ Plan Lifecycle List Accepts Filter Flags
     Should Be Equal As Integers    ${result.rc}    0
     Should Contain    ${result.stdout}    plan-cli-list-filters-ok
 
+Plan Lifecycle List Accepts Regex Positional Argument
+    [Documentation]    Verify that ``plan list <REGEX>`` filters plans by name regex
+    ${result}=    Run Process    ${PYTHON}    ${HELPER}    list-regex    cwd=${WORKSPACE}
+    Log    ${result.stdout}
+    Log    ${result.stderr}
+    Should Be Equal As Integers    ${result.rc}    0
+    Should Contain    ${result.stdout}    plan-cli-list-regex-ok
+
 Plan Status Renders Required Fields
     [Documentation]    Verify that ``plan status`` renders action_name, phase, state, projects, args, timestamps
     ${result}=    Run Process    ${PYTHON}    ${HELPER}    status-fields    cwd=${WORKSPACE}