feat(native): harden launcher bridge and implement presentation-aware handover

- Upgraded LauncherBackgroundSync to force-hydrate OS metadata (home/tmp) on mount.
- Hardened electron_relay.ts with robust placeholder resolution and global regex.
- Restored safe handover by making native.launch_from_cache presentation-aware.
- Integrated heartbeat and sync status into the formal Launcher Config UI.
- Added comprehensive technical documentation for the 2026 native architecture.

src/lib/stores/ae_events_stores.ts

@@ -400,6 +400,18 @@ const events_session_data_struct: key_val = {
         event_file_open: {}, // This is from the older Launcher.
         native: {},
 
+        // Shared observability for Sync Monitor and Config Drawer
+        sync_stats: {
+            total: 0,
+            cached: 0,
+            missing: 0,
+            currently_syncing: null
+        },
+        heartbeat_info: {
+            last_timestamp: null,
+            status: 'pending'
+        },
+
         modal__title: '',
         modal__open_event_file_id: false,
         modal__event_file_obj: null,