fix(migration): show startup preparation and recover source read failures (#1568)

* fix(migration): show startup preparation and recover source read failures

* fix(migration): keep inventory reload failures recoverable

* test(migration): type the deferred recovery hook

* fix(migration): reconcile failed EPG cleanup before recovery

* fix(migration): await settings before inventory readiness

* style(migration): add a subtle theme-aware startup watermark

apps/web/src/app/app.component.html

@@ -1,4 +1,7 @@
-<router-outlet />
+<app-startup-status #startup [routeReady]="routeReady()" />
+<div [style.display]="startup.complete() ? 'contents' : 'none'">
+    <router-outlet (activate)="routeReady.set(true)" />
+</div>
 
 <app-epg-progress-panel />