fix: resolve all 15 frontend ESLint errors for green CI

- Replace setState-in-effect with state-based tracking (AdminLayout, EditCategoryModal)
- Convert inline SortIcon component to getSortIcon function (TreeTableView)
- Remove unused catch parameters (CreateCategoryModal, EditCategoryModal)
- Replace `any` types with proper types (SessionFilters, AdminCategoriesPage, SessionHistoryPage)
- Fix unused destructuring variable (StepRatingModal)
- Fix constant binary expression in test (utils.test.ts)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/lib/utils.test.ts

@@ -7,7 +7,8 @@ describe('cn', () => {
   })
 
   it('handles conditional classes', () => {
-    expect(cn('base', false && 'hidden', 'visible')).toBe('base visible')
+    const isHidden = false
+    expect(cn('base', isHidden && 'hidden', 'visible')).toBe('base visible')
   })
 
   it('deduplicates tailwind classes', () => {