fix(desktop): Lotus links use the public web app, and open in-app (#248)

Lotus permalinks (#130) were built from window.location.origin. In the
desktop app that's the local tauri-plugin-localhost server (hash-routed), so
"Copy Lotus Link" copied e.g. http://localhost:…/#/home/!room…, which works
for nobody else. And the link recogniser only knew that local base, so a real
https://chat.lotusguild.org/home/… link in a message opened the browser
instead of the room.

- useLotusShareBase: in the desktop app, links for other people use config
  `webAppUrl` (https only, set by cinny-desktop #23) in web path-routing
  form; otherwise the origin, as before. Used by "Copy Lotus Link" on
  messages, the space menu and space tabs.
- The recogniser accepts several bases: the origin, plus `webAppUrl` in the
  desktop app.
- The web app is unchanged.

Verified with a simulated desktop (Tauri bridge + webAppUrl) against a local
Synapse. Copied links are https://chat.lotusguild.org/home/<room>/<event> and
https://chat.lotusguild.org/<space>. A public link in a message renders as
the room pill and clicking it opens the room in-app, with nothing sent to the
system browser. The web app still copies origin links. Unit tests for the
base selection; Playwright 20 passed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/pages/client/sidebar/SpaceTabs.tsx

@@ -49,13 +49,7 @@ import { roomToParentsAtom } from '../../../state/room/roomToParents';
 import { allRoomsAtom } from '../../../state/room-list/roomList';
 import { useAnyRoomLiveCall } from '../../../hooks/useSpaceLiveCall';
 import { LiveDot } from './SpaceTabs.css';
-import {
-  getOriginBaseUrl,
-  getSpaceLobbyPath,
-  getSpacePath,
-  joinPathComponent,
-} from '../../pathUtils';
-import { useClientConfig } from '../../../hooks/useClientConfig';
+import { getSpaceLobbyPath, getSpacePath, joinPathComponent } from '../../pathUtils';
 import {
   SidebarAvatar,
   SidebarItem,
@@ -102,6 +96,7 @@ import { settingsAtom } from '../../../state/settings';
 import { useOpenSpaceSettings } from '../../../state/hooks/spaceSettings';
 import { useRoomCreators } from '../../../hooks/useRoomCreators';
 import { useRoomPermissions } from '../../../hooks/useRoomPermissions';
+import { useLotusShareBase } from '../../../hooks/useLotusLinkBase';
 import { InviteUserPrompt } from '../../../components/invite-user-prompt';
 
 type SpaceMenuProps = {
@@ -112,7 +107,7 @@ type SpaceMenuProps = {
 const SpaceMenu = forwardRef<HTMLDivElement, SpaceMenuProps>(
   ({ room, requestClose, onUnpin }, ref) => {
     const mx = useMatrixClient();
-    const { hashRouter } = useClientConfig();
+    const lotusBase = useLotusShareBase();
     const [hideActivity] = useSetting(settingsAtom, 'hideActivity');
     const roomToParents = useAtomValue(roomToParentsAtom);
     const powerLevels = usePowerLevels(room);
@@ -152,9 +147,7 @@ const SpaceMenu = forwardRef<HTMLDivElement, SpaceMenuProps>(
     const handleCopyLotusLink = () => {
       const roomIdOrAlias = getCanonicalAliasOrRoomId(mx, room.roomId);
       const viaServers = isRoomAlias(roomIdOrAlias) ? undefined : getViaServers(room);
-      copyToClipboard(
-        getLotusSpacePermalink(getOriginBaseUrl(hashRouter), roomIdOrAlias, viaServers),
-      );
+      copyToClipboard(getLotusSpacePermalink(lotusBase, roomIdOrAlias, viaServers));
       requestClose();
     };