fix(event_session): restore event_presentation/presenter_li_qry_str fields

These fields from v_event_session_w_file_count were lost during the v1/v2
-> v3 migration. Added to Event_Session_Base model and to searchable_fields
in the event_session object definition.

Fields are only available via the alt view (v_event_session_w_file_count).
To search: use ?view=alt on the nested search endpoint.
To retrieve: use ?inc_file_count=true on the GET endpoint.

Also:
- Updated ARCH__V3_DEVELOPMENT_STANDARDS.md: expanded Field Evolution
  Checklist with alt-view field rules, Docker restart requirement, and
  documented the ?view= parameter as a live (not proposed) feature.
- Updated TODO__Agents.md: marked migration gap audit as complete.
- Added regression test to test_e2e_v3_search_engine.py.

app/object_definitions/events_presentation.py

@@ -135,7 +135,8 @@ events_presentation_obj_li = {
             'poc_person_full_name',
             'public', 'public_hide', 'hide_event_launcher',
             'priority', 'sort', 'group', 'notes', 'created_on', 'updated_on',
-            'default_qry_str', 'event_location_name'
+            'default_qry_str', 'event_location_name',
+            'event_presentation_li_qry_str', 'event_presenter_li_qry_str'
         ],
     },
     'event_track': {