feat: add recurring event deletion with three modes

Implement three deletion modes for recurring events:
- single: exclude specific occurrence via EXDATE mechanism
- future: set RRULE UNTIL to stop future occurrences
- all: delete entire event series

Changes include:
- Add exceptionDates field to CalendarEvent model
- Add RecurringDeleteMode type and DeleteRecurringEventDTO
- EventService.deleteRecurring() with mode-based logic using rrule library
- EventController DELETE endpoint accepts mode/occurrenceDate query params
- recurrenceExpander filters out exception dates during expansion
- AI tools support deleteMode and occurrenceDate for proposed deletions
- ChatService.confirmEvent() handles recurring delete modes
- New DeleteEventModal component for unified delete confirmation UI
- Calendar screen integrates modal for both recurring and non-recurring events

apps/client/src/components/DeleteEventModal.tsx

@@ -0,0 +1,162 @@
+import { Modal, Pressable, Text, View } from "react-native";
+import { RecurringDeleteMode } from "@calchat/shared";
+import { useThemeStore } from "../stores/ThemeStore";
+
+type DeleteEventModalProps = {
+  visible: boolean;
+  eventTitle: string;
+  isRecurring: boolean;
+  onConfirm: (mode: RecurringDeleteMode) => void;
+  onCancel: () => void;
+};
+
+type DeleteOption = {
+  mode: RecurringDeleteMode;
+  label: string;
+  description: string;
+};
+
+const RECURRING_DELETE_OPTIONS: DeleteOption[] = [
+  {
+    mode: "single",
+    label: "Nur dieses Vorkommen",
+    description: "Nur der ausgewaehlte Termin wird entfernt",
+  },
+  {
+    mode: "future",
+    label: "Dieses und zukuenftige",
+    description: "Dieser und alle folgenden Termine werden entfernt",
+  },
+  {
+    mode: "all",
+    label: "Alle Vorkommen",
+    description: "Die gesamte Terminserie wird geloescht",
+  },
+];
+
+export const DeleteEventModal = ({
+  visible,
+  eventTitle,
+  isRecurring,
+  onConfirm,
+  onCancel,
+}: DeleteEventModalProps) => {
+  const { theme } = useThemeStore();
+
+  return (
+    <Modal
+      visible={visible}
+      transparent={true}
+      animationType="fade"
+      onRequestClose={onCancel}
+    >
+      <Pressable
+        className="flex-1 justify-center items-center"
+        style={{ backgroundColor: "rgba(0,0,0,0.5)" }}
+        onPress={onCancel}
+      >
+        <Pressable
+          className="w-11/12 rounded-2xl overflow-hidden"
+          style={{
+            backgroundColor: theme.primeBg,
+            borderWidth: 4,
+            borderColor: theme.borderPrimary,
+          }}
+          onPress={(e) => e.stopPropagation()}
+        >
+          {/* Header */}
+          <View
+            className="px-4 py-3"
+            style={{
+              backgroundColor: theme.chatBot,
+              borderBottomWidth: 3,
+              borderBottomColor: theme.borderPrimary,
+            }}
+          >
+            <Text
+              className="font-bold text-lg"
+              style={{ color: theme.textPrimary }}
+            >
+              {isRecurring
+                ? "Wiederkehrenden Termin loeschen"
+                : "Termin loeschen"}
+            </Text>
+            <Text style={{ color: theme.textSecondary }} numberOfLines={1}>
+              {eventTitle}
+            </Text>
+          </View>
+
+          {/* Content */}
+          <View className="p-4">
+            {isRecurring ? (
+              // Recurring event: show three options
+              RECURRING_DELETE_OPTIONS.map((option) => (
+                <Pressable
+                  key={option.mode}
+                  onPress={() => onConfirm(option.mode)}
+                  className="py-3 px-4 rounded-lg mb-2"
+                  style={{
+                    backgroundColor: theme.secondaryBg,
+                    borderWidth: 1,
+                    borderColor: theme.borderPrimary,
+                  }}
+                >
+                  <Text
+                    className="font-medium text-base"
+                    style={{ color: theme.textPrimary }}
+                  >
+                    {option.label}
+                  </Text>
+                  <Text
+                    className="text-sm mt-1"
+                    style={{ color: theme.textMuted }}
+                  >
+                    {option.description}
+                  </Text>
+                </Pressable>
+              ))
+            ) : (
+              // Non-recurring event: simple confirmation
+              <View>
+                <Text
+                  className="text-base mb-4"
+                  style={{ color: theme.textPrimary }}
+                >
+                  Möchtest du diesen Termin wirklich löschen?
+                </Text>
+                <Pressable
+                  onPress={() => onConfirm("all")}
+                  className="py-3 px-4 rounded-lg"
+                  style={{
+                    backgroundColor: theme.rejectButton,
+                  }}
+                >
+                  <Text
+                    className="font-medium text-base text-center"
+                    style={{ color: theme.buttonText }}
+                  >
+                    Loeschen
+                  </Text>
+                </Pressable>
+              </View>
+            )}
+          </View>
+
+          {/* Cancel button */}
+          <Pressable
+            onPress={onCancel}
+            className="py-3 items-center"
+            style={{
+              borderTopWidth: 1,
+              borderTopColor: theme.placeholderBg,
+            }}
+          >
+            <Text style={{ color: theme.primeFg }} className="font-bold">
+              Abbrechen
+            </Text>
+          </Pressable>
+        </Pressable>
+      </Pressable>
+    </Modal>
+  );
+};