Enhance: Implement exhaustive background caching and recursive data loading

- Implemented aggressive room-wide background caching engine in LauncherBackgroundSync.svelte.
- Added inc_file_li and inc_all_file_li support to Event and Event Location object loaders for total room coverage.
- Switched to proven V1 download path (/hosted_file/) to resolve V3 CRUD binary delivery issues.
- Optimized Electron bridge with download locking and flat-hash storage matching legacy 'perfect' logic.
- Standardized all Electron IPC methods and parameters to snake_case.
- Added visual sync progress indicator for room caching status.

src/lib/ae_events/ae_events__event.ts

@@ -10,6 +10,7 @@ import { load_ae_obj_li__event_device } from './ae_events__event_device';
 import { load_ae_obj_li__event_location } from './ae_events__event_location';
 import { load_ae_obj_li__event_session } from './ae_events__event_session';
 import { load_ae_obj_li__event_badge_template } from '$lib/ae_events/ae_events__event_badge_template';
+import { load_ae_obj_li__event_file } from '$lib/ae_events/ae_events__event_file';
 
 const ae_promises: key_val = {};