fix(ag-ui): collapse overlay actually hides content (:host selector)

Live map smoke caught that the collapse toggled the host class but the
day content stayed visible: `.itin--collapsed [cdkDropListGroup]` can't
match a host-level class under Angular emulated encapsulation (the
selector gets _ngcontent appended; the host carries _nghost). Use
:host(.itin--collapsed) so the descendant hide-rules apply. The P2.11
unit test only asserted the host class toggles, not that content hides,
so it passed while the visual collapse was broken.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: blove

examples/ag-ui/angular/src/app/itinerary-panel.component.ts

@@ -456,11 +456,11 @@ import { ItineraryStop, ItineraryStore } from './itinerary-store';
         background: var(--ngaf-chat-surface-alt);
         color: var(--ngaf-chat-text);
       }
-      .itin--collapsed [cdkDropListGroup],
-      .itin--collapsed .itin__add-day-btn {
+      :host(.itin--collapsed) [cdkDropListGroup],
+      :host(.itin--collapsed) .itin__add-day-btn {
         display: none;
       }
-      .itin--collapsed .itin__head {
+      :host(.itin--collapsed) .itin__head {
         margin-bottom: 0;
       }
     `,