fix(pres_mgmt): hidden files now visible in Manage Files without manual refresh

Background file loads for session, presentation, and presenter were using the
default hidden='not_hidden', so hidden files never reached Dexie. The Manage
Files liveQuery reads straight from Dexie, making hidden files completely
invisible until the Refresh button was clicked (which already used hidden='all').

The Launcher is unaffected — it has always had a render-time guard that hides
files with event_file_obj.hide unless show_content__hidden_files is enabled.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/ae_events/ae_events__event_session.ts

@@ -278,6 +278,10 @@ async function _handle_nested_loads(
                 for_obj_type: 'event_session',
                 for_obj_id: current_session_id,
                 enabled,
+                // WHY: must include hidden files so the Manage Files UI can show and unhide them.
+                // The default 'not_hidden' was causing hidden files to never reach Dexie,
+                // making them invisible in the manage list until a manual Refresh.
+                hidden: 'all',
                 limit: 15,
                 try_cache,
                 log_lvl