feat(ui): show the email upgrade box to guests

Un-hide the Profile email box for guest accounts (hidden={!p.isGuest}): a guest
binds an email to register / sign in, and a returning address opens the existing
merge dialog. Provider linking stays hidden — the Telegram control keeps its
wiring behind a hidden attribute — until the non-guest linking matrix (PR2). The
two linking e2e specs remain skipped (they assume a non-guest login and the
visible Telegram control); update their stale comments.

ui/src/screens/Profile.svelte

@@ -244,10 +244,11 @@
       </form>
     {/if}
 
-    <!-- Linking & merge. Hidden for now: we target provider sign-in, and the anonymous
-         /app/ guest (whose upgrade path this is) comes later. Kept wired — drop `hidden`
-         to re-enable, together with the skipped linking specs in e2e/social.spec.ts. -->
-    <section class="emailbox" hidden>
+    <!-- The guest's email upgrade path: bind an email to register / sign in (a returning
+         address triggers the merge dialog below). Guest-only for now; provider linking
+         (Add VK / Add Telegram / Unlink) and the non-guest matrix come next, together
+         with the skipped linking specs in e2e/social.spec.ts. -->
+    <section class="emailbox" hidden={!p.isGuest}>
       <h3>{t('profile.linkAccount')}</h3>
       {#if !emailSent}
         <div class="addrow">
@@ -272,7 +273,8 @@
         </div>
       {/if}
       {#if telegramLinkable}
-        <button class="ghost tg" onclick={linkTelegram} disabled={!connection.online}>{t('profile.linkTelegram')}</button>
+        <!-- Provider linking lands with the non-guest matrix (PR2); kept wired but hidden. -->
+        <button class="ghost tg" hidden onclick={linkTelegram} disabled={!connection.online}>{t('profile.linkTelegram')}</button>
       {/if}
     </section>