test(session): add TDD failing tests for session create DI error

Implement TDD bug-capture tests for bug #570 where `agents session create`
fails because `_get_session_service()` calls `container.db()` which does
not exist on the DI Container class (AttributeError). Same root cause as
bug #554.

Behave BDD scenarios tagged @tdd_bug @tdd_bug_570 @tdd_expected_fail
exercise the real DI path (no mocks). Includes Robot Framework integration
smoke tests with self-inverting helper and ASV benchmark baseline.

ISSUES CLOSED: #631

noxfile.py

@@ -252,7 +252,7 @@ def _has_failures(total):
 
 
 def _no_scenarios_ran(total):
-    """Return True when the runner collected zero scenario results.
+    """Return True when no scenario reached a terminal state.
 
     This catches runner-level crashes (e.g. ``before_all`` failure) that
     prevent any scenario from executing.  Without this guard the summary