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/dto/task-recurrence.ts

@@ -0,0 +1,22 @@
+export type TaskRecurrence = {
+    id: number
+    '@id'?: string
+    type: 'daily' | 'weekly' | 'monthly' | 'yearly'
+    interval: number
+    daysOfWeek: string[] | null
+    dayOfMonth: number | null
+    weekOfMonth: number | null
+    endDate: string | null
+    maxOccurrences: number | null
+    occurrenceCount: number
+}
+
+export type TaskRecurrenceWrite = {
+    type: 'daily' | 'weekly' | 'monthly' | 'yearly'
+    interval: number
+    daysOfWeek?: string[] | null
+    dayOfMonth?: number | null
+    weekOfMonth?: number | null
+    endDate?: string | null
+    maxOccurrences?: number | null
+}