fix: resolve all 8 pre-existing lint errors (closes #29)

Fixed @typescript-eslint/no-explicit-any (4 occurrences):
- FolderEditModal.tsx: proper error type checking instead of any
- StepForm.tsx: explicit union type for visibility select
- StepLibraryBrowser.tsx: explicit union types for stepType and sortBy selects

Fixed react-hooks/set-state-in-effect (1 occurrence):
- NodeEditorModal.tsx: replaced useEffect with direct state comparison

Fixed @typescript-eslint/no-unused-vars (3 occurrences):
- NodeEditorModal.tsx: removed unused useEffect import
- NodeEditorModal.tsx: added eslint-disable for intentionally destructured children
- usePermissions.ts: removed unused _tree parameter from canDeleteTree
- TreeLibraryPage.tsx: updated canDeleteTree call site

Fixed @typescript-eslint/no-empty-object-type (1 occurrence):
- types/step.ts: changed empty interface to type alias

Verification:
- npm run lint: 0 errors (9 warnings are intentional exhaustive-deps)
- npm run build: succeeds
- TypeScript compilation: passes

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

frontend/src/types/step.ts

@@ -119,6 +119,5 @@ export interface Rating {
   user_name?: string
 }
 
-export interface Review extends Rating {
-  // Same as Rating, just an alias for clarity
-}
+// Review is an alias for Rating
+export type Review = Rating