fix(desktop): relay host status, display, and server-side LAN candidate

- Probe relay hosts through a throwaway E2EE tunnel in the host switcher
  instead of an HTTP probe against the relay:// pseudo-URL, which always
  reported Unreachable
- Show 'via OpenChamber Relay' for relay hosts in the switcher and the
  servers list instead of the raw relay:// pseudo-URL; hide the URL-centric
  edit action for relay hosts (saving it would drop the tunnel descriptor)
- Pairing LAN candidate prefers the address the requesting client actually
  reached the server on; interface scanning could pick an unroutable virtual
  bridge (docker0), producing links whose LAN leg silently failed and forced
  devices onto the relay

packages/ui/src/components/desktop/DesktopHostSwitcher.tsx

@@ -450,6 +450,13 @@ export function DesktopHostSwitcherDialog({
       const localClientToken = await getLocalClientToken();
       const results = await Promise.all(
         hosts.map(async (h) => {
+          // Relay hosts have no HTTP address to probe — check reachability
+          // through a throwaway E2EE tunnel instead.
+          if (h.relay) {
+            const startedAt = performance.now();
+            const ok = await probeRelayHost(h.relay).catch(() => false);
+            return [h.id, { status: ok ? ('ok' as const) : ('unreachable' as const), latencyMs: Math.round(performance.now() - startedAt) } satisfies HostStatus] as const;
+          }
           const url = normalizeHostUrl(isElectronShell() ? getDesktopHostApiUrl(h) : h.url);
           if (!url) {
             return [h.id, { status: 'unreachable' as const, latencyMs: 0 } satisfies HostStatus] as const;
@@ -898,7 +905,9 @@ export function DesktopHostSwitcherDialog({
                 const displayLabel = host.id === LOCAL_HOST_ID
                   ? t('desktopHostSwitcher.instance.local')
                   : redactSensitiveUrl(host.label);
-                const displayUrl = redactSensitiveUrl(effectiveUrl);
+                // Relay hosts have a relay:// pseudo-URL that means nothing to a
+                // person — say how the connection works instead.
+                const displayUrl = host.relay ? t('mobile.connect.relay.badge') : redactSensitiveUrl(effectiveUrl);
 
                 return (
                   <div

packages/ui/src/components/sections/remote-instances/RemoteInstancesPage.tsx

@@ -1459,16 +1459,23 @@ export const RemoteInstancesPage: React.FC = () => {
                           <p className="typography-ui-label text-foreground truncate">{redactSensitiveUrl(host.label)}</p>
                           {directDefaultHostId === host.id ? <span className="typography-micro text-muted-foreground">{t('desktopHostSwitcher.header.default')}</span> : null}
                         </div>
-                        <p className="typography-micro text-muted-foreground font-mono truncate">{redactSensitiveUrl(host.apiUrl || host.url)}</p>
+                        <p className={cn('typography-micro text-muted-foreground truncate', !host.relay && 'font-mono')}>
+                          {host.relay ? t('mobile.connect.relay.badge') : redactSensitiveUrl(host.apiUrl || host.url)}
+                        </p>
                       </div>
                       <div className="flex shrink-0 items-center gap-1">
                         <Button type="button" variant="ghost" size="xs" className="!font-normal" onClick={() => void setDefaultDirectHost(host.id)} disabled={directSaving || directDefaultHostId === host.id} aria-label={t('desktopHostSwitcher.actions.setAsDefaultAria')}>
                           {directDefaultHostId === host.id ? <Icon name="star-fill" className="h-3.5 w-3.5" /> : <Icon name="star" className="h-3.5 w-3.5" />}
                         </Button>
-                        <Button type="button" variant="ghost" size="xs" className="!font-normal" onClick={() => beginEditDirectHost(host)} disabled={directSaving}>
-                          <Icon name="pencil" className="h-3.5 w-3.5" />
-                          {t('desktopHostSwitcher.actions.edit')}
-                        </Button>
+                        {/* The edit form is URL/token-centric; saving it would drop a
+                            relay host's tunnel descriptor. Relay hosts are re-imported
+                            via a fresh pairing link instead. */}
+                        {host.relay ? null : (
+                          <Button type="button" variant="ghost" size="xs" className="!font-normal" onClick={() => beginEditDirectHost(host)} disabled={directSaving}>
+                            <Icon name="pencil" className="h-3.5 w-3.5" />
+                            {t('desktopHostSwitcher.actions.edit')}
+                          </Button>
+                        )}
                         <Button type="button" variant="ghost" size="xs" className="!font-normal" onClick={() => void handleRemoveDirectHost(host.id)} disabled={directSaving}>
                           <Icon name="delete-bin" className="h-3.5 w-3.5" />
                           {t('settings.common.actions.delete')}