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/files/folder-tree-sidebar.tsx

@@ -208,7 +208,7 @@ function FolderTreeItem({
 }) {
   const isExpanded = expandedIds.has(node.id);
   const isSelected = currentPath === node.path;
-  const isLoading = loadingIds.has(node.id);
+  const _isLoading = loadingIds.has(node.id);
   const children = childrenCache.get(node.id);
   const hasChildren = children !== undefined && children.length > 0;
   const indentPx = depth * 16;