Add bot-driven room app UI via im.paarrot.ui state.

Bots can publish a declarative panel UI that takes over a room; user
actions are sent as im.paarrot.ui.action timeline events.

src/app/features/room-app/RoomAppView.tsx

@@ -0,0 +1,67 @@
+import React, { useCallback } from 'react';
+import { Box, Button, Header, Text, config } from 'folds';
+import { Room } from 'matrix-js-sdk';
+import { Page } from '../../components/page';
+import { useMatrixClient } from '../../hooks/useMatrixClient';
+import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
+import { useStateEvent } from '../../hooks/useStateEvent';
+import { useRoomName } from '../../hooks/useRoomMeta';
+import {
+  MessageEvent,
+  PaarrotUiActionContent,
+  StateEvent,
+} from '../../../types/matrix/room';
+import { parsePaarrotUiContent } from '../../utils/room';
+import { RoomAppSchema } from './RoomAppSchema';
+import * as css from './RoomAppView.css';
+
+type RoomAppViewProps = {
+  room: Room;
+  onShowChat: () => void;
+};
+
+export function RoomAppView({ room, onShowChat }: RoomAppViewProps) {
+  const mx = useMatrixClient();
+  const useAuthentication = useMediaAuthentication();
+  const roomName = useRoomName(room);
+  const uiEvent = useStateEvent(room, StateEvent.PaarrotUi);
+  const content = parsePaarrotUiContent(uiEvent?.getContent());
+  const title = content?.title || roomName || 'Room App';
+
+  const handleAction = useCallback(
+    async (payload: PaarrotUiActionContent) => {
+      await mx.sendEvent(room.roomId, MessageEvent.PaarrotUiAction as any, payload);
+    },
+    [mx, room.roomId]
+  );
+
+  return (
+    <Page>
+      <Header className={css.Header} size="600">
+        <Box grow="Yes" alignItems="Center" gap="200">
+          <Box grow="Yes" alignItems="Center" gap="200" minWidth="0">
+            <Text size="H6" truncate>
+              {title}
+            </Text>
+          </Box>
+          <Button size="300" variant="Secondary" radii="300" onClick={onShowChat}>
+            <Text size="B300">Show chat</Text>
+          </Button>
+        </Box>
+      </Header>
+      <Box className={css.Body} grow="Yes" direction="Column" style={{ gap: config.space.S400 }}>
+        {content ? (
+          <RoomAppSchema
+            mx={mx}
+            content={content}
+            uiEventId={uiEvent?.getId()}
+            useAuthentication={useAuthentication}
+            onAction={handleAction}
+          />
+        ) : (
+          <Text size="T400">This room’s app UI is missing or invalid.</Text>
+        )}
+      </Box>
+    </Page>
+  );
+}