feat(ui): one-tap confirm deeplink screen + client language

Add the /confirm/<token> SPA route and Confirm screen: a prefetch-safe button
POSTs the token via a new confirmEmailLink RPC (client/transport/mock/codec +
ConfirmLinkResult model). A login adopts the minted session and enters the app; a
link shows confirmed / merge-in-the-app; an invalid or expired token asks for a new
code. Exempt /confirm from the no-session /login redirect. Forward the client
locale on the email request (authEmailRequest gains language → app.locale) so a
fresh web login email is localised. Handle the new 'profile' live-event sub-kind by
re-fetching the profile, so a link confirmed in another browser reflects in-app at
once. i18n en+ru.

ui/src/screens/Confirm.svelte

@@ -0,0 +1,95 @@
+<script lang="ts">
+  import { confirmDeeplink } from '../lib/app.svelte';
+  import { t } from '../lib/i18n/index.svelte';
+
+  let { token }: { token: string } = $props();
+  // idle → busy → (login navigates away) | linked | merge | error. The token is
+  // confirmed only on the button press (a POST), so a mail scanner prefetching the
+  // link (a GET on the SPA route) never consumes it.
+  let stage = $state<'idle' | 'busy' | 'linked' | 'merge' | 'error'>('idle');
+
+  async function confirm(): Promise<void> {
+    if (!token) {
+      stage = 'error';
+      return;
+    }
+    stage = 'busy';
+    try {
+      const r = await confirmDeeplink(token);
+      // A login has already navigated into the app; a link stays here with a result.
+      stage = r === 'merge_required' ? 'merge' : 'linked';
+    } catch {
+      stage = 'error';
+    }
+  }
+</script>
+
+<main class="confirm">
+  <div class="card">
+    <div class="brand">{t('app.title')}</div>
+    {#if stage === 'idle' || stage === 'busy'}
+      <p>{t('confirm.prompt')}</p>
+      <button class="primary" disabled={stage === 'busy'} onclick={confirm}>
+        {t('confirm.action')}
+      </button>
+    {:else if stage === 'linked'}
+      <p class="ok">{t('confirm.linked')}</p>
+      <p class="muted">{t('confirm.close')}</p>
+    {:else if stage === 'merge'}
+      <p class="ok">{t('confirm.merge')}</p>
+      <p class="muted">{t('confirm.close')}</p>
+    {:else}
+      <p class="err">{t('confirm.expired')}</p>
+    {/if}
+  </div>
+</main>
+
+<style>
+  .confirm {
+    height: 100%;
+    display: grid;
+    place-items: center;
+    padding: 16px;
+  }
+  .card {
+    width: min(94vw, 360px);
+    background: var(--surface);
+    border: 1px solid var(--border);
+    border-radius: var(--radius);
+    box-shadow: var(--shadow);
+    padding: 24px;
+    display: flex;
+    flex-direction: column;
+    gap: 12px;
+    text-align: center;
+  }
+  .brand {
+    font-weight: 700;
+    letter-spacing: 0.04em;
+    color: var(--accent);
+  }
+  p {
+    margin: 0;
+  }
+  .muted {
+    color: var(--text-muted);
+    font-size: 0.9rem;
+  }
+  .ok {
+    font-weight: 600;
+  }
+  .err {
+    color: var(--danger, #c0392b);
+  }
+  button {
+    padding: 12px;
+    border-radius: var(--radius-sm);
+    border: 1px solid var(--accent);
+    font-weight: 600;
+    background: var(--accent);
+    color: var(--accent-text);
+  }
+  button:disabled {
+    opacity: 0.5;
+  }
+</style>