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/controllers/EventController.ts

@@ -1,4 +1,5 @@
 import { Response } from "express";
+import { RecurringDeleteMode } from "@calchat/shared";
 import { EventService } from "../services";
 import { createLogger } from "../logging";
 import { AuthenticatedRequest } from "./AuthMiddleware";
@@ -72,7 +73,10 @@ export class EventController {
       );
       res.json(events);
     } catch (error) {
-      log.error({ error, start: req.query.start, end: req.query.end }, "Error getting events by range");
+      log.error(
+        { error, start: req.query.start, end: req.query.end },
+        "Error getting events by range",
+      );
       res.status(500).json({ error: "Failed to get events" });
     }
   }
@@ -97,6 +101,38 @@ export class EventController {
 
   async delete(req: AuthenticatedRequest, res: Response): Promise<void> {
     try {
+      const { mode, occurrenceDate } = req.query as {
+        mode?: RecurringDeleteMode;
+        occurrenceDate?: string;
+      };
+
+      // If mode is specified, use deleteRecurring
+      if (mode) {
+        const result = await this.eventService.deleteRecurring(
+          req.params.id,
+          req.user!.userId,
+          mode,
+          occurrenceDate,
+        );
+
+        // For 'all' mode or when event was completely deleted, return 204
+        if (result === null && mode === "all") {
+          res.status(204).send();
+          return;
+        }
+
+        // For 'single' or 'future' modes, return updated event
+        if (result) {
+          res.json(result);
+          return;
+        }
+
+        // result is null but mode wasn't 'all' - event not found or was deleted
+        res.status(204).send();
+        return;
+      }
+
+      // Default behavior: delete completely
       const deleted = await this.eventService.delete(
         req.params.id,
         req.user!.userId,