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/app/event/[id].tsx

@@ -19,27 +19,49 @@ const EventDetailScreen = () => {
   return (
     <BaseBackground>
       <View className="flex-1 p-4">
-        <Text className="text-2xl mb-4" style={{ color: theme.textPrimary }}>Event Detail</Text>
-        <Text className="mb-4" style={{ color: theme.textSecondary }}>ID: {id}</Text>
+        <Text className="text-2xl mb-4" style={{ color: theme.textPrimary }}>
+          Event Detail
+        </Text>
+        <Text className="mb-4" style={{ color: theme.textSecondary }}>
+          ID: {id}
+        </Text>
         <TextInput
           placeholder="Title"
           placeholderTextColor={theme.textMuted}
           className="w-full border rounded p-2 mb-4"
-          style={{ color: theme.textPrimary, borderColor: theme.borderPrimary, backgroundColor: theme.secondaryBg }}
+          style={{
+            color: theme.textPrimary,
+            borderColor: theme.borderPrimary,
+            backgroundColor: theme.secondaryBg,
+          }}
         />
         <TextInput
           placeholder="Description"
           placeholderTextColor={theme.textMuted}
           multiline
           className="w-full border rounded p-2 mb-4 h-24"
-          style={{ color: theme.textPrimary, borderColor: theme.borderPrimary, backgroundColor: theme.secondaryBg }}
+          style={{
+            color: theme.textPrimary,
+            borderColor: theme.borderPrimary,
+            backgroundColor: theme.secondaryBg,
+          }}
         />
         <View className="flex-row gap-2">
-          <Pressable className="p-3 rounded flex-1" style={{ backgroundColor: theme.confirmButton }}>
-            <Text className="text-center" style={{ color: theme.buttonText }}>Save</Text>
+          <Pressable
+            className="p-3 rounded flex-1"
+            style={{ backgroundColor: theme.confirmButton }}
+          >
+            <Text className="text-center" style={{ color: theme.buttonText }}>
+              Save
+            </Text>
           </Pressable>
-          <Pressable className="p-3 rounded flex-1" style={{ backgroundColor: theme.rejectButton }}>
-            <Text className="text-center" style={{ color: theme.buttonText }}>Delete</Text>
+          <Pressable
+            className="p-3 rounded flex-1"
+            style={{ backgroundColor: theme.rejectButton }}
+          >
+            <Text className="text-center" style={{ color: theme.buttonText }}>
+              Delete
+            </Text>
           </Pressable>
         </View>
       </View>