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/layout/icon-picker.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useState, useMemo, useRef, useEffect, useCallback } from 'react';
+import { useState, useMemo, useRef, useCallback } from 'react';
 import { useTranslations } from 'next-intl';
 import { icons as lucideIcons, type LucideIcon } from 'lucide-react';
 import { Search, X } from 'lucide-react';