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/editor/Editor.tsx

@@ -256,7 +256,7 @@ export const CustomEditor = forwardRef<HTMLDivElement, CustomEditorProps>(
               className={css.EditorTextareaScroll}
               variant="SurfaceVariant"
               style={scrollStyle}
-              size="300"
+              size="0"
               visibility="Hover"
               hideTrack
               ref={editableRef}