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/RoomInput.css.ts

@@ -6,7 +6,8 @@ export const RoomInputWrap = style({
   width: '100%',
 });
 
-globalStyle(`${RoomInputWrap} .${editorCss.Editor}`, {
+/* Notebook-flat composer chrome — Stationery only (other themes keep Editor inset border) */
+globalStyle(`.stationery ${RoomInputWrap} .${editorCss.Editor}`, {
   borderRadius: 0,
   boxShadow: 'none',
   borderTop: `${config.borderWidth.B300} solid ${color.SurfaceVariant.ContainerLine}`,