feat(ui) : add DTOs and services for calendar fields, recurrence, and Zimbra settings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/services/zimbra.ts

@@ -0,0 +1,21 @@
+import type { ZimbraSettings, ZimbraSettingsWrite, ZimbraTestResult } from './dto/zimbra'
+
+export function useZimbraService() {
+    const api = useApi()
+
+    async function getSettings(): Promise<ZimbraSettings> {
+        return api.get<ZimbraSettings>('/settings/zimbra')
+    }
+
+    async function saveSettings(payload: ZimbraSettingsWrite): Promise<ZimbraSettings> {
+        return api.put<ZimbraSettings>('/settings/zimbra', payload as Record<string, unknown>, {
+            toastSuccessKey: 'zimbra.settings.saved',
+        })
+    }
+
+    async function testConnection(): Promise<ZimbraTestResult> {
+        return api.post<ZimbraTestResult>('/settings/zimbra/test', {})
+    }
+
+    return { getSettings, saveSettings, testConnection }
+}