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/hooks/useLotusLinkBase.test.ts

@@ -0,0 +1,23 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { lotusLinkBases, lotusShareBase } from './useLotusLinkBase';
+
+const LOCAL = 'http://localhost:44548/#/';
+const WEB = 'https://chat.lotusguild.org';
+
+test('web: shared links use the page origin', () => {
+  assert.equal(lotusShareBase(WEB, false, WEB), WEB);
+  assert.deepEqual(lotusLinkBases(WEB, false, undefined), [WEB]);
+});
+
+test('desktop with webAppUrl: shared links use the public web app', () => {
+  assert.equal(lotusShareBase(LOCAL, true, `${WEB}/`), WEB);
+  assert.deepEqual(lotusLinkBases(LOCAL, true, WEB), [LOCAL, WEB]);
+});
+
+test('desktop without a valid webAppUrl falls back to the origin', () => {
+  [undefined, '', 'http://chat.lotusguild.org', 'nonsense'].forEach((v) => {
+    assert.equal(lotusShareBase(LOCAL, true, v), LOCAL, String(v));
+    assert.deepEqual(lotusLinkBases(LOCAL, true, v), [LOCAL]);
+  });
+});

src/app/hooks/useLotusLinkBase.ts

@@ -0,0 +1,37 @@
+import { useMemo } from 'react';
+import { useClientConfig } from './useClientConfig';
+import { isTauri } from './useTauri';
+import { getOriginBaseUrl } from '../pages/pathUtils';
+import { resolveWebAppUrl } from '../utils/callInBrowser';
+
+/**
+ * [Gitea #248] Base URL for Lotus links meant for other people.
+ *
+ * On the web that's this page's origin. In the desktop app the page is served
+ * from a local address (and hash-routed), which nobody else can open, so use
+ * the public web app from config `webAppUrl` (web path routing) instead.
+ * Without a valid `webAppUrl` it falls back to the origin, as before.
+ */
+export const lotusShareBase = (originBase: string, desktop: boolean, webAppUrl: unknown): string =>
+  (desktop && resolveWebAppUrl(webAppUrl)) || originBase;
+
+/**
+ * Every base a Lotus link to this deployment may start with: the origin, plus
+ * the public web app in the desktop app, so a shared https link opens in-app.
+ */
+export const lotusLinkBases = (
+  originBase: string,
+  desktop: boolean,
+  webAppUrl: unknown,
+): string[] => {
+  const shared = lotusShareBase(originBase, desktop, webAppUrl);
+  return shared === originBase ? [originBase] : [originBase, shared];
+};
+
+export const useLotusShareBase = (): string => {
+  const { hashRouter, webAppUrl } = useClientConfig();
+  return useMemo(
+    () => lotusShareBase(getOriginBaseUrl(hashRouter), isTauri(), webAppUrl),
+    [hashRouter, webAppUrl],
+  );
+};