fix(email): match IMAP card to SMTP styling + auto-detect mailbox folders

- IncomingMailConfigCard rebuilt to mirror the outgoing SMTP card: Card
  padding=md, icon inputs (Server/User/Lock), password eye toggle, stacked
  full-width fields, full-width primary Save button
- Folder is now a dropdown auto-populated by a 'Detect' button instead of a
  free-text path: backend emailIntakeService.listFolders() lists IMAP
  mailboxes (POST /admin/email/incoming-config/folders, accepts current form
  creds, masked password falls back to stored); UI auto-selects the inbox
  (special-use) folder
- en/de strings added

backend/src/services/emailIntakeService.js

@@ -48,6 +48,41 @@ async function saveAttachment(att) {
   return filePath;
 }
 
+/**
+ * List the mailbox folders on the IMAP server so the UI can offer a
+ * dropdown instead of a free-text path. Uses the saved config; an
+ * `override` ({ host, port, secure, user, pass }) lets the admin detect
+ * folders BEFORE saving. A masked/blank override password falls back to
+ * the stored one. Returns [{ path, name, specialUse }] (specialUse like
+ * '\\Inbox' lets the caller auto-select the inbox).
+ */
+async function listFolders(override) {
+  let cfg;
+  if (override && override.host && override.user) {
+    cfg = {
+      host: override.host,
+      port: override.port || 993,
+      secure: override.secure !== false && override.secure !== 0,
+      auth: { user: override.user, pass: override.pass || '' },
+    };
+    if (!cfg.auth.pass || cfg.auth.pass === '********') {
+      const stored = await getImapConfig();
+      cfg.auth.pass = stored?.auth?.pass || '';
+    }
+  } else {
+    cfg = await getImapConfig();
+  }
+  if (!cfg) return [];
+  const client = new ImapFlow({ host: cfg.host, port: cfg.port, secure: cfg.secure, auth: cfg.auth, logger: false });
+  await client.connect();
+  try {
+    const list = await client.list();
+    return (list || []).map((m) => ({ path: m.path, name: m.name, specialUse: m.specialUse || null }));
+  } finally {
+    await client.logout().catch(() => {});
+  }
+}
+
 /** Poll the mailbox once. Safe to call repeatedly; self-skips when busy/off. */
 async function pollOnce() {
   if (polling) return { skipped: 'busy' };
@@ -120,4 +155,4 @@ function startIncomingMailPoller() {
   logger.info?.('Incoming-mail poller started (every 60s when enabled)');
 }
 
-module.exports = { pollOnce, startIncomingMailPoller, _internal: { getImapConfig, isEnabled, saveAttachment } };
+module.exports = { pollOnce, startIncomingMailPoller, listFolders, _internal: { getImapConfig, isEnabled, saveAttachment } };