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/server/src/ai/utils/toolDefinitions.ts

@@ -140,7 +140,7 @@ export const TOOL_DEFINITIONS: ToolDefinition[] = [
   {
     name: "proposeDeleteEvent",
     description:
-      "Propose deleting an event. The user must confirm. Use this when the user wants to remove an appointment.",
+      "Propose deleting an event. The user must confirm. Use this when the user wants to remove an appointment. For recurring events, specify deleteMode to control which occurrences to delete.",
     parameters: {
       type: "object",
       properties: {
@@ -148,6 +148,17 @@ export const TOOL_DEFINITIONS: ToolDefinition[] = [
           type: "string",
           description: "ID of the event to delete",
         },
+        deleteMode: {
+          type: "string",
+          enum: ["single", "future", "all"],
+          description:
+            "For recurring events: 'single' = only this occurrence, 'future' = this and all future, 'all' = entire recurring event. Defaults to 'all' for non-recurring events.",
+        },
+        occurrenceDate: {
+          type: "string",
+          description:
+            "ISO date string (YYYY-MM-DD) of the specific occurrence to delete. Required for 'single' and 'future' modes.",
+        },
       },
       required: ["eventId"],
     },