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/components/message/layout/layout.css.ts

@@ -242,6 +242,7 @@ export const MessageTextBody = recipe({
         lineHeight: 1,
         overflow: 'visible',
         overflowY: 'visible',
+        paddingBottom: config.space.S200,
       },
     },
     emote: {