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/routes/events/[event_id]/(launcher)/launcher_background_sync.svelte

@@ -43,6 +43,12 @@
                 if (info) {
                     $ae_loc.home_directory = info.home_directory;
                     $ae_loc.tmp_directory = info.tmp_directory;
+                    
+                    // Also sync into native_device for redundancy
+                    if (!$ae_loc.native_device) $ae_loc.native_device = {};
+                    $ae_loc.native_device.home_directory = info.home_directory;
+                    $ae_loc.native_device.tmp_directory = info.tmp_directory;
+                    
                     if (log_lvl) console.log('Sync: Native OS metadata hydrated.', { home: info.home_directory });
                 }
             } catch (err) {