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/+layout.ts

@@ -148,6 +148,12 @@ export async function load({ fetch, params, parent, route, url }) {
                     ae_loc_init['host_file_temp_path'] = native_device_config.native_device.host_file_temp_path;
                     ae_loc_init['recording_path'] = native_device_config.native_device.recording_path;
                 }
+
+                // IMPORTANT: Update API settings with the native-authorized key if present
+                if (native_device_config.aether_api_key) {
+                    ae_api_init['api_secret_key'] = native_device_config.aether_api_key;
+                    ae_api_headers['x-aether-api-key'] = native_device_config.aether_api_key;
+                }
             }
         } catch (err) {
             console.error('ROOT LOAD: Failed to fetch native device config.', err);