fix(tui): correct cycle_persona test fixture to use non-cycleable default persona

The step_register_cycleable_personas fixture was using the first cycleable
persona (alpha, cycle_order=1) as the registry default. When cycle_persona
was called with no active session, _resolve_default_name() resolved to alpha
(which IS in the cycleable list at index 0), causing the implementation to
advance to beta instead of starting from alpha as the test expected.

Fix: use a dedicated non-cycleable default persona (cycle_order=0) so that
_resolve_default_name() returns default (not in the cycleable list),
making current_idx=-1 and cycling correctly starts from index 0 (alpha).

This resolves the unit_tests CI failure introduced in the previous commit.

features/steps/tui_persona_state_coverage_steps.py

@@ -380,18 +380,27 @@ def step_verify_cycle_persona_result(context, expected):
 
 @given('cycleable personas "{names_csv}" are registered for session "{session_id}"')
 def step_register_cycleable_personas(context, names_csv, session_id):
-    """Register multiple cycleable personas with ascending cycle_order values."""
+    """Register multiple cycleable personas with ascending cycle_order values.
+
+    A non-cycleable "default" persona is used as the registry default so that
+    when no active persona has been set for the session, ``_resolve_default_name``
+    returns "default" (not in the cycleable list).  This means the first call to
+    ``cycle_persona`` starts from the beginning of the cycleable list (index 0).
+    """
     names = [n.strip() for n in names_csv.split(",")]
     registry = MagicMock()
     personas = [
         Persona(name=name, actor="ns/actor", cycle_order=idx + 1)
         for idx, name in enumerate(names)
     ]
+    # Non-cycleable default persona — ensures _resolve_default_name() returns a
+    # name that is NOT in the cycleable list, so cycling starts from index 0.
+    default_persona = Persona(name="default", actor="ns/actor", cycle_order=0)
     registry.list_personas.return_value = personas
     registry.get.side_effect = lambda name: next(
         (p for p in personas if p.name == name), None
     )
-    registry.ensure_default.return_value = personas[0]
+    registry.ensure_default.return_value = default_persona
     registry.get_last_persona.return_value = None
     registry.set_last_persona = MagicMock()
     context.state = PersonaState(registry=registry)