fix(room-preview): make the preview card actually populate + richer

Two review agents found the preview card degrades to 'id + logo + Join' for real
reasons. Fixes:

- **via was dropped at the summary fetch** (root cause). RoomSummaryLoader now
  accepts + forwards `via` to getRoomSummary (and keys the query on it);
  JoinBeforeNavigate passes viaServers; the lobby Preview chip carries data-via and
  Lobby.handleOpenRoom appends it to the navigated URL. Without this, previews of
  rooms the HS isn't already in came back sparse/404.
- **No loading/error state** -> RoomSummaryLoader now surfaces {loading,error};
  JoinBeforeNavigate shows a Spinner while loading instead of the degraded card.
- **Room id leaked as name AND topic AND header** -> stop using the raw `!id` as
  the topic fallback (show 'No description'); name falls back to canonical_alias
  then alias-localpart; the page header shows the summary name.
- **Richer, membership-aware card**: forward canonical_alias (shown under the name),
  world_readable ('Readable' badge), and membership -> the button now shows Accept
  invite / Requested / Banned correctly instead of a Join that lies; a 'hero' layout
  for the single-preview page (primary Join button, unclamped topic). Removed dead
  `|| undefined ||`.

IRoomSummary re-adds canonical_alias (the SDK type Omit<>s it though MSC3266
returns it). 738 tests pass, build clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/lobby/Lobby.tsx

@@ -36,7 +36,7 @@ import { useCategoryHandler } from '../../hooks/useCategoryHandler';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { allRoomsAtom } from '../../state/room-list/roomList';
 import { getCanonicalAliasOrRoomId, rateLimitedActions } from '../../utils/matrix';
-import { getSpaceRoomPath } from '../../pages/pathUtils';
+import { getSpaceRoomPath, withSearchParam } from '../../pages/pathUtils';
 import { StateEvent } from '../../../types/matrix/room';
 import { CanDropCallback, useDnDMonitor } from './DnD';
 import { ASCIILexicalTable, orderKeys } from '../../utils/ASCIILexicalTable';
@@ -411,8 +411,13 @@ export function Lobby() {
   const handleOpenRoom: MouseEventHandler<HTMLButtonElement> = (evt) => {
     const rId = evt.currentTarget.getAttribute('data-room-id');
     if (!rId) return;
+    // Preview chips carry the room's resident servers so getRoomSummary can
+    // resolve a room the homeserver isn't already in (else the preview is sparse).
+    const via = evt.currentTarget.getAttribute('data-via');
     const pSpaceIdOrAlias = getCanonicalAliasOrRoomId(mx, space.roomId);
-    navigate(getSpaceRoomPath(pSpaceIdOrAlias, getCanonicalAliasOrRoomId(mx, rId)));
+    let path = getSpaceRoomPath(pSpaceIdOrAlias, getCanonicalAliasOrRoomId(mx, rId));
+    if (via) path = withSearchParam(path, { viaServers: via });
+    navigate(path);
   };
 
   const togglePinToSidebar = useCallback(

src/app/features/lobby/RoomItem.tsx

@@ -102,14 +102,17 @@ function RoomJoinButton({ roomId, via }: RoomJoinButtonProps) {
 // room isn't joined — renders the preview card instead of the timeline.
 function RoomPreviewChip({
   roomId,
+  via,
   onOpen,
 }: {
   roomId: string;
+  via?: string[];
   onOpen: MouseEventHandler<HTMLButtonElement>;
 }) {
   return (
     <Chip
       data-room-id={roomId}
+      data-via={via && via.length > 0 ? via.join(',') : undefined}
       onClick={onOpen}
       variant="Secondary"
       fill="None"
@@ -391,7 +394,7 @@ export const RoomItemCard = as<'div', RoomItemCardProps>(
                       </Box>
                     ) : (
                       <Box shrink="No" gap="100" alignItems="Center">
-                        <RoomPreviewChip roomId={roomId} onOpen={onOpen} />
+                        <RoomPreviewChip roomId={roomId} via={content.via} onOpen={onOpen} />
                         <RoomJoinButton roomId={roomId} via={content.via} />
                       </Box>
                     )
@@ -439,7 +442,7 @@ export const RoomItemCard = as<'div', RoomItemCardProps>(
                   joinRule={summary.join_rule}
                   options={
                     <Box shrink="No" gap="100" alignItems="Center">
-                      <RoomPreviewChip roomId={roomId} onOpen={onOpen} />
+                      <RoomPreviewChip roomId={roomId} via={content.via} onOpen={onOpen} />
                       <RoomJoinButton roomId={roomId} via={content.via} />
                     </Box>
                   }