Fix: Restore Native caching business logic and implement 3-mode launcher

- Implemented Default, Onsite, and Native launcher modes in launcher_file_cont.svelte.
- Restored background pre-caching logic with configurable timers in new LauncherBackgroundSync component.
- Fixed standard browser download regression for regular website mode.
- Modernized electron_relay to TypeScript and standardized bridge detection in layout.
- Detailed startup and background sync technical flow in documentation.

src/routes/events/[event_id]/(launcher)/launcher_session_view.svelte

@@ -83,7 +83,7 @@
             // Check if results are different than the current $events_slct.event_file_obj_li
             if ($events_slct.event_file_obj_li && results) {
                 if (JSON.stringify($events_slct.event_file_obj_li) !== JSON.stringify(results)) {
-                    $events_slct.event_file_obj_li = { ...results };
+                    $events_slct.event_file_obj_li = [...results];
                     if (log_lvl) {
                         console.log(
                             `$events_slct.event_file_obj_li has changed for event_session_id: ${slct__event_session_id}`,
@@ -97,6 +97,8 @@
                         );
                     }
                 }
+            } else if (results) {
+                $events_slct.event_file_obj_li = [...results];
             }
 
             return results;