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)

lib/demo/fixtures/emails.ts

@@ -2,8 +2,6 @@ import type { Email } from '@/lib/jmap/types';
 import { demoDate } from '../demo-utils';
 
 export function createDemoEmails(): Email[] {
-  const now = new Date();
-
   return [
     // ── Inbox ───────────────────────────────────────────────────
     {