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.

documentation/TODO__Agents.md

@@ -34,6 +34,7 @@
     - [x] Whitelist `account_id` in all Event search definitions.
     - [x] Audit Relational "Low-Priority" Models (Address, Contact, DataStore).
     - [x] **V3 Uniform Lookup System:** Phase 1 & 2 Complete.
+    - [x] **Restore alt-view convenience fields lost in v1→v3 migration (May 2026):** `site_domain` (`account_name`, `account_code`, `account_enable`, `account_enable_from/to`, `site_enable_from/to`, `site_domain_access_key`, `logo_path`, `style_href`, `script_src`, `google_tracking_id`) and `event_session` (`event_presentation_li_qry_str`, `event_presenter_li_qry_str`). Fields added to Pydantic models and `searchable_fields`. Alt-view fields require `?view=alt` for search.
     - [ ] Verify SQL Views join in all required `_random` IDs for performance.
 - [ ] **Step 2:** Coordination (Verify Frontend uses `x-account-id` instead of token).
 - [ ] **Step 3:** Frontend V3 WebSocket integration test — queued after IDAA-specific work. Backend is ready (auth wired, heartbeat presence refresh confirmed, unit tests passing). Frontend guide updated at `GUIDE__AE_API_V3_for_Frontend_websockets.md`.