Show a crash outside a page instead of a white screen

Moving between pages sometimes left a white screen until a reload: an
error outside the page's own error boundary (the layout, the sign-in
gate) unmounted the whole app. An error boundary now wraps the whole
app, shows the error's name and message, and tries again when the route
changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/components/ErrorBoundary.tsx

@@ -3,10 +3,15 @@ import { t } from '../i18n'
 import { Empty } from './Page'
 
 // Without this, one component throwing while rendering unmounts the whole app and leaves a white
-// page. The layout keys it by route, so moving to another page clears the error.
-export class ErrorBoundary extends Component<{ children: ReactNode }, { error: Error | null }> {
+// page. The layout keys it by route, so moving to another page clears the error; main.tsx also puts
+// one around the whole app (the layout included), cleared by a change of `resetKey`.
+export class ErrorBoundary extends Component<{ children: ReactNode; resetKey?: string; className?: string }, { error: Error | null }> {
   state = { error: null as Error | null }
 
+  componentDidUpdate(prev: { resetKey?: string }) {
+    if (this.state.error && prev.resetKey !== this.props.resetKey) this.setState({ error: null })
+  }
+
   static getDerivedStateFromError(error: Error) {
     return { error }
   }
@@ -19,11 +24,11 @@ export class ErrorBoundary extends Component<{ children: ReactNode }, { error: E
     const { error } = this.state
     if (!error) return this.props.children
     return (
-      <div className="card">
+      <div className={this.props.className ?? 'card'}>
         <Empty icon="info" title={t('err.crashTitle')}>
           {t('err.crashCopy')}
           <br />
-          <small>{error.message}</small>
+          <small>{error.name}: {error.message}</small>
         </Empty>
         <div style={{ display: 'flex', justifyContent: 'center', gap: 8, paddingBottom: 24 }}>
           <button className="btn small" onClick={() => this.setState({ error: null })}>{t('common.retry')}</button>