feat(mail): rich text editor for signatures + placeholder variables

- Replace textarea in SignatureManager with TipTap RichTextEditor
- Add placeholder variable buttons: {{user.name}}, {{user.first_name}},
  {{user.last_name}}, {{user.email}}, {{user.role}}, {{tenant.name}}, {{date}}
- Add replaceSignatureVariables() utility in mail API
- ComposeModal now replaces variables with actual user/tenant data when inserting signature
- Variables resolved from auth store (user name, email, role, tenant name)

frontend/src/api/mail.ts

@@ -417,6 +417,31 @@ export function decodeMimeHeader(value: string | undefined | null): string {
   }
 }
 
+/**
+ * Replace placeholder variables in signature HTML with actual user/tenant data.
+ * Variables: {{user.name}}, {{user.first_name}}, {{user.last_name}},
+ * {{user.email}}, {{user.role}}, {{tenant.name}}, {{date}}
+ */
+export function replaceSignatureVariables(
+  html: string,
+  user: { name?: string; email?: string; role?: string; first_name?: string; last_name?: string },
+  tenant?: { name?: string },
+): string {
+  const now = new Date();
+  const dateStr = now.toLocaleDateString([], { year: 'numeric', month: '2-digit', day: '2-digit' });
+  const firstName = user.first_name || (user.name ? user.name.split(' ')[0] : '');
+  const lastName = user.last_name || (user.name ? user.name.split(' ').slice(1).join(' ') : '');
+
+  return html
+    .replace(/\{\{user\.name\}\}/gi, user.name || '')
+    .replace(/\{\{user\.first_name\}\}/gi, firstName)
+    .replace(/\{\{user\.last_name\}\}/gi, lastName)
+    .replace(/\{\{user\.email\}\}/gi, user.email || '')
+    .replace(/\{\{user\.role\}\}/gi, user.role || '')
+    .replace(/\{\{tenant\.name\}\}/gi, tenant?.name || '')
+    .replace(/\{\{date\}\}/gi, dateStr);
+}
+
 // ─── Folders ────────────────────────────────────────────────────────────────
 
 export function fetchFolders(accountId: string): Promise<MailFolder[]> {

frontend/src/components/mail/ComposeModal.tsx

@@ -12,7 +12,8 @@ import { Select } from '@/components/ui/Select';
 import { TemplatePicker } from './TemplatePicker';
 import { RichTextEditor } from './RichTextEditor';
 import type { Mail, MailSignature, SendMailPayload, ReplyPayload, ForwardPayload, MailDraftPayload } from '@/api/mail';
-import { uploadAttachment, type UploadedAttachment } from '@/api/mail';
+import { uploadAttachment, type UploadedAttachment, replaceSignatureVariables } from '@/api/mail';
+import { useAuthStore } from '@/store/authStore';
 
 export type ComposeMode = 'new' | 'reply' | 'forward' | 'draft';
 
@@ -42,6 +43,8 @@ export function ComposeModal({
   onClose,
 }: ComposeModalProps) {
   const { t } = useTranslation();
+  const authUser = useAuthStore((s) => s.user);
+  const authTenant = useAuthStore((s) => s.currentTenant);
   const [to, setTo] = useState('');
   const [cc, setCc] = useState('');
   const [bcc, setBcc] = useState('');
@@ -87,9 +90,14 @@ export function ComposeModal({
     setSelectedSignatureId(signatureId);
     const sig = signatures.find((s) => s.id === signatureId);
     if (sig) {
-      setBody((prev) => `${prev}<br/><br/>---<br/>${sig.body_html}`);
+      const processedHtml = replaceSignatureVariables(
+        sig.body_html,
+        { name: authUser?.name, email: authUser?.email, role: authUser?.role, first_name: authUser?.first_name, last_name: authUser?.last_name },
+        { name: authTenant?.name },
+      );
+      setBody((prev) => `${prev}<br/><br/>---<br/>${processedHtml}`);
     }
-  }, [signatures]);
+  }, [signatures, authUser, authTenant]);
 
   const handleTemplateSelect = useCallback((templateBody: string, templateSubject: string) => {
     setBody(templateBody);

frontend/src/components/mail/SignatureManager.tsx

@@ -1,5 +1,6 @@
 /**
- * Signature manager — CRUD for mail signatures.
+ * Signature manager — CRUD for mail signatures with rich text editor.
+ * Supports placeholder variables for user/tenant data.
  */
 
 import React, { useState, useEffect, useCallback } from 'react';
@@ -10,6 +11,7 @@ import { Card } from '@/components/ui/Card';
 import { EmptyState } from '@/components/ui/EmptyState';
 import { useToast } from '@/components/ui/Toast';
 import { ConfirmDialog } from '@/components/ui/ConfirmDialog';
+import { RichTextEditor } from './RichTextEditor';
 import {
   fetchSignatures,
   createSignature,
@@ -18,6 +20,17 @@ import {
   type MailSignature,
 } from '@/api/mail';
 
+/** Available placeholder variables for signatures. */
+const SIGNATURE_VARIABLES = [
+  { token: '{{user.name}}', label: 'Vollständiger Name', description: 'Max Mustermann' },
+  { token: '{{user.first_name}}', label: 'Vorname', description: 'Max' },
+  { token: '{{user.last_name}}', label: 'Nachname', description: 'Mustermann' },
+  { token: '{{user.email}}', label: 'E-Mail', description: 'max@firma.de' },
+  { token: '{{user.role}}', label: 'Rolle', description: 'Admin' },
+  { token: '{{tenant.name}}', label: 'Firma/Organisation', description: 'HMS Licht & Ton' },
+  { token: '{{date}}', label: 'Aktuelles Datum', description: '16.07.2026' },
+];
+
 export function SignatureManager() {
   const { t } = useTranslation();
   const toast = useToast();
@@ -134,12 +147,24 @@ export function SignatureManager() {
             />
             <div>
               <label className="block text-sm font-medium text-secondary-700 mb-1">{t('mail.signatureBody')}</label>
-              <textarea
-                value={bodyHtml}
-                onChange={(e) => setBodyHtml(e.target.value)}
-                className="w-full min-h-24 border border-secondary-300 rounded-md p-3 text-sm focus:outline-none focus:ring-2 focus:ring-primary-500"
-                placeholder="<p>Regards, John</p>"
-                data-testid="signature-body"
+              {/* Placeholder variable buttons */}
+              <div className="flex flex-wrap gap-1 mb-2" data-testid="signature-variables">
+                {SIGNATURE_VARIABLES.map((v) => (
+                  <button
+                    key={v.token}
+                    type="button"
+                    onClick={() => setBodyHtml((prev) => `${prev}${v.token}`)}
+                    className="inline-flex items-center px-2 py-0.5 text-xs rounded border border-secondary-300 bg-secondary-50 hover:bg-secondary-100 text-secondary-700"
+                    title={v.description}
+                  >
+                    {v.label} <code className="ml-1 text-primary-600">{v.token}</code>
+                  </button>
+                ))}
+              </div>
+              <RichTextEditor
+                content={bodyHtml}
+                onChange={setBodyHtml}
+                placeholder="<p>Mit freundlichen Grüßen,<br>{{user.name}}</p>"
               />
             </div>
             <label className="flex items-center gap-2 text-sm text-secondary-700">