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/routes/events/[event_id]/(launcher)/+layout.svelte

@@ -0,0 +1,21 @@
+<script lang="ts">
+    /**
+     * events/[event_id]/(launcher)/+layout.svelte
+     * Root layout for the launcher area. 
+     * Ensures background sync runs globally regardless of active tab.
+     */
+    import { ae_loc } from '$lib/stores/ae_stores';
+    import LauncherBackgroundSync from './launcher_background_sync.svelte';
+
+    interface Props {
+        children?: import('svelte').Snippet;
+    }
+
+    let { children }: Props = $props();
+</script>
+
+<!-- Background Sync Process (Invisible) -->
+<LauncherBackgroundSync log_lvl={1} />
+
+<!-- Render the rest of the launcher UI -->
+{@render children?.()}