Add Shared Media drawer and harden same-room navigation.

Widen the media panel, support skinny full-page mode, keep jump-to-latest and return-to-previous reliable, and stop same-room event jumps from remounting the outlet or yanking the sidebar.

src/app/features/room/RoomTimeline.css.ts

@@ -9,7 +9,8 @@ export const TimelineFloat = recipe({
       position: 'absolute',
       left: '50%',
       transform: 'translateX(-50%)',
-      zIndex: 1,
+      // Above timeline media carousels / sticky message chrome
+      zIndex: 10,
       minWidth: 'max-content',
     },
   ],