fix: resolve all 69 ESLint warnings across 40 files

- Remove unused imports (Mail, CalendarIcon, Plus, Circle, cn, Link,
  MessageCircle, User, Tag, FolderUp, useEffect, LogOut, GripVertical,
  Check, X, HoverActionsMode, HoverActionsCorner, asn1js, Convert, etc.)
- Prefix unused variables/params with underscore to satisfy no-unused-vars
- Add missing React hook dependencies (exhaustive-deps)
- Wrap handleNavigateUp in useCallback and selectedGroupMembers in useMemo
- Remove unused eslint-disable directives in jmap/client.ts
- Replace as any with typed casts in filter-store and smime-store tests
- Remove dead code (macOk assignment, unused now variable)

components/calendar/task-modal.tsx

@@ -6,7 +6,7 @@ import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { X, Trash2, CalendarDays, Bell, Flag } from "lucide-react";
 import { format, parseISO } from "date-fns";
-import { cn } from "@/lib/utils";
+
 import type { CalendarTask, Calendar, CalendarEventAlert } from "@/lib/jmap/types";
 
 interface TaskModalProps {
@@ -43,7 +43,7 @@ export function TaskModal({
   onSave,
   onDelete,
   onClose,
-  isMobile,
+  isMobile: _isMobile,
 }: TaskModalProps) {
   const t = useTranslations("calendar");
   const isEdit = !!task;