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/components/library/FolderEditModal.tsx

@@ -159,8 +159,11 @@ export function FolderEditModal({
       onClose()
       // Dispatch event to refresh folder list
       window.dispatchEvent(new Event('folder-changed'))
-    } catch (err: any) {
-      setError(err.response?.data?.detail || 'Failed to save folder')
+    } catch (err) {
+      const errorMessage = err instanceof Error && 'response' in err
+        ? (err as { response?: { data?: { detail?: string } } }).response?.data?.detail
+        : undefined
+      setError(errorMessage || 'Failed to save folder')
     } finally {
       setIsSubmitting(false)
     }

frontend/src/components/step-library/StepForm.tsx

@@ -356,7 +356,7 @@ export function StepForm({ onSubmit, onCancel, initialData }: StepFormProps) {
         <select
           id="visibility"
           value={visibility}
-          onChange={(e) => setVisibility(e.target.value as any)}
+          onChange={(e) => setVisibility(e.target.value as 'private' | 'team' | 'public')}
           className="w-full rounded-md border border-input bg-background px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-ring"
         >
           <option value="private">Private (only me)</option>

frontend/src/components/step-library/StepLibraryBrowser.tsx

@@ -164,7 +164,7 @@ export function StepLibraryBrowser({ onInsert, onCreateNew, showCreateButton = f
           <select
             aria-label="Filter by step type"
             value={selectedStepType || ''}
-            onChange={(e) => setSelectedStepType((e.target.value as any) || undefined)}
+            onChange={(e) => setSelectedStepType((e.target.value as 'decision' | 'action' | 'solution') || undefined)}
             className="rounded-md border border-input bg-background px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-ring"
           >
             <option value="">All Types</option>
@@ -190,7 +190,7 @@ export function StepLibraryBrowser({ onInsert, onCreateNew, showCreateButton = f
           <select
             aria-label="Sort steps by"
             value={sortBy}
-            onChange={(e) => setSortBy(e.target.value as any)}
+            onChange={(e) => setSortBy(e.target.value as 'recent' | 'popular' | 'highest_rated' | 'most_used')}
             className="rounded-md border border-input bg-background px-3 py-2 text-sm focus:outline-none focus:ring-2 focus:ring-ring"
           >
             <option value="recent">Most Recent</option>

frontend/src/components/tree-editor/NodeEditorModal.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback } from 'react'
+import { useState, useCallback } from 'react'
 import { Modal } from '@/components/common/Modal'
 import { useTreeEditorStore } from '@/store/treeEditorStore'
 import { NodeFormDecision } from './NodeFormDecision'
@@ -18,12 +18,14 @@ export function NodeEditorModal({ node, onClose, isNewNode = false }: NodeEditor
   const nodeErrors = validationErrors.filter(e => e.nodeId === node.id)
 
   // Local draft state - changes are NOT persisted until "Done" is clicked
+  // Reset draft when node ID changes (switching to a different node)
   const [draft, setDraft] = useState<TreeStructure>(() => structuredClone(node))
+  const [lastNodeId, setLastNodeId] = useState(node.id)
 
-  // Reset draft when node changes (e.g., external update)
-  useEffect(() => {
+  if (node.id !== lastNodeId) {
     setDraft(structuredClone(node))
-  }, [node.id]) // Only reset when switching to a different node
+    setLastNodeId(node.id)
+  }
 
   const handleUpdate = useCallback((updates: Partial<TreeStructure>) => {
     setDraft(prev => ({ ...prev, ...updates }))
@@ -33,6 +35,7 @@ export function NodeEditorModal({ node, onClose, isNewNode = false }: NodeEditor
     // Commit all draft changes to the store
     // IMPORTANT: Exclude 'children' from the update - children are managed separately
     // by addNode/deleteNode and we don't want to overwrite them with stale draft data
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
     const { children, ...draftWithoutChildren } = draft
     updateNode(node.id, draftWithoutChildren)
     onClose()

frontend/src/hooks/usePermissions.ts

@@ -55,7 +55,7 @@ export function usePermissions() {
       return false
     },
 
-    canDeleteTree: (_tree: { author_id: string | null }) => {
+    canDeleteTree: () => {
       if (!user) return false
       return user.is_super_admin
     },

frontend/src/pages/TreeLibraryPage.tsx

@@ -364,7 +364,7 @@ export function TreeLibraryPage() {
                           <Pencil className="h-4 w-4" />
                         </Link>
                       )}
-                      {canDeleteTree({ author_id: tree.author_id }) && (
+                      {canDeleteTree() && (
                         <button
                           type="button"
                           onClick={() => {

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