Add tree organization system with categories, tags, and folders

Features:
- Categories: Global and team-specific tree categorization (admin-managed)
- Tags: Flexible tree tagging with autocomplete (author + admin)
- User folders: Personal tree collections with subfolder support
  - Hierarchical structure (max 3 levels deep)
  - Right-click context menu for folder management
  - Cascade delete for subfolders
- Filter trees by category, tags, and folder in library view

Backend:
- New models: Category, Tag, UserFolder with relationships
- New API endpoints for categories, tags, and folders
- Tree organization migrations (005, 006)

Frontend:
- FolderSidebar with hierarchical folder tree
- FolderEditModal for create/edit with color picker
- AddToFolderMenu for quick tree organization
- TagInput with autocomplete and TagBadges display
- Updated TreeMetadataForm and TreeLibraryPage

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/api/categories.ts

@@ -0,0 +1,32 @@
+import apiClient from './client'
+import type { Category, CategoryListItem, CategoryCreate, CategoryUpdate } from '@/types'
+
+export const categoriesApi = {
+  async list(includeInactive = false, teamOnly = false): Promise<CategoryListItem[]> {
+    const response = await apiClient.get<CategoryListItem[]>('/categories', {
+      params: { include_inactive: includeInactive, team_only: teamOnly },
+    })
+    return response.data
+  },
+
+  async get(id: string): Promise<Category> {
+    const response = await apiClient.get<Category>(`/categories/${id}`)
+    return response.data
+  },
+
+  async create(data: CategoryCreate): Promise<Category> {
+    const response = await apiClient.post<Category>('/categories', data)
+    return response.data
+  },
+
+  async update(id: string, data: CategoryUpdate): Promise<Category> {
+    const response = await apiClient.put<Category>(`/categories/${id}`, data)
+    return response.data
+  },
+
+  async delete(id: string): Promise<void> {
+    await apiClient.delete(`/categories/${id}`)
+  },
+}
+
+export default categoriesApi