fix(auth,webmail): list a pre-accounts session in the switcher; preview as plain text

A browser signed in before account cookies existed has only lm_user_session,
so the switcher showed it as loading forever. The active session now always
counts and is filed on first listing. Message previews drop the HTML and
entities the server stored.

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

services/webmail/src/app/(user)/user/mail/[folder]/page.tsx

@@ -28,6 +28,7 @@ import {
   type ListFilter,
 } from "../../../../../lib/mailCounts";
 import { sanitizeEmailHtml, blockRemoteImages, unblockRemoteImages } from "../../../../../lib/sanitizer";
+import { plainSnippet } from "../../../../../lib/snippet";
 import { isSenderTrusted, trustSender, revokeSender } from "../../../../../lib/remoteImages";
 import { resolveInlineImages, buildReaderDocument, type InlineImages } from "../../../../../lib/emailBody";
 import { Button } from "../../../../../components/ui/Button";
@@ -545,7 +546,7 @@ export default function MailFolderPage({ params }: { params: Promise<{ folder: s
                       {msg.subject || t("mail.noSubject")}
                     </span>
                     <span className="line-clamp-2 text-xs leading-relaxed text-slate-400 [overflow-wrap:anywhere]">
-                      {msg.snippet}
+                      {plainSnippet(msg.snippet)}
                     </span>
                     {msg.has_attachments && (
                       <span className="mt-px flex items-center gap-1.5">