feat(quick-260914-m97): Feld Fehlermeldungen an im SMTP-Formular — settings-api, Formular, i18n settings.smtp

- SmtpConfig.bugReportRecipient (string | null) und SaveSmtpPayload.bugReportRecipient (null loescht, fehlend bewahrt)
- Eingabefeld type=email hinter der Absenderadresse mit Hinweistext; Payload traegt immer trim() || null
- Zwei Komponententests: Vorbelegung aus GET, PUT-Payload mit Wert bzw. null
- i18n settings.smtp.bugReportRecipient / bugReportRecipientHelp in de und en

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018N9CD3ebPKm1b32bPpBknY

apps/web/src/components/settings/smtp-settings-form.tsx

@@ -23,6 +23,7 @@ interface FormState {
   username: string;
   password: string; // T-07-17: always starts blank; never pre-filled from server
   fromAddress: string;
+  bugReportRecipient: string; // quick-260914-m97: Postfach fuer den Fehler-melden-Knopf
 }
 
 const DEFAULT_FORM: FormState = {
@@ -32,6 +33,7 @@ const DEFAULT_FORM: FormState = {
   username: '',
   password: '',
   fromAddress: '',
+  bugReportRecipient: '',
 };
 
 type TestFeedback =
@@ -70,6 +72,7 @@ export function SmtpSettingsForm() {
             username: config.username ?? '',
             password: '', // T-07-17: never pre-filled
             fromAddress: config.fromAddress,
+            bugReportRecipient: config.bugReportRecipient ?? '',
           });
         }
       })
@@ -95,6 +98,8 @@ export function SmtpSettingsForm() {
     if (form.username.trim()) payload.username = form.username.trim();
     // T-07-17: only include password when user has typed a new one
     if (form.password) payload.password = form.password;
+    // quick-260914-m97: das Formular ist der einzige Klient — leer bedeutet loeschen (null)
+    payload.bugReportRecipient = form.bugReportRecipient.trim() || null;
     return payload;
   };
 
@@ -300,6 +305,26 @@ export function SmtpSettingsForm() {
         </p>
       </div>
 
+      {/* Fehlermeldungen an (quick-260914-m97) */}
+      <div>
+        <label htmlFor="smtp-bug-report-recipient" className={labelClass}>
+          {t('smtp.bugReportRecipient')}
+        </label>
+        <input
+          id="smtp-bug-report-recipient"
+          type="email"
+          placeholder="fehler@example.com"
+          className={inputClass}
+          value={form.bugReportRecipient}
+          onChange={(e) =>
+            setForm((prev) => ({ ...prev, bugReportRecipient: e.target.value }))
+          }
+        />
+        <p className="mt-1 text-xs text-muted-foreground">
+          {t('smtp.bugReportRecipientHelp')}
+        </p>
+      </div>
+
       {/* Test-E-Mail Empfänger */}
       <div>
         <label htmlFor="smtp-test-to" className={labelClass}>