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>

backend/app/schemas/__init__.py

@@ -2,10 +2,23 @@ from .user import UserCreate, UserUpdate, UserResponse, UserLogin
 from .token import Token, TokenPayload
 from .tree import TreeCreate, TreeUpdate, TreeResponse, TreeListResponse
 from .session import SessionCreate, SessionUpdate, SessionResponse, SessionExport, DecisionRecord
+from .category import CategoryCreate, CategoryUpdate, CategoryResponse, CategoryListResponse
+from .tag import TagCreate, TagResponse, TagListResponse, TagAssignment
+from .folder import FolderCreate, FolderUpdate, FolderResponse, FolderListResponse, FolderReorderRequest, FolderTreeRequest
 
 __all__ = [
+    # User
     "UserCreate", "UserUpdate", "UserResponse", "UserLogin",
+    # Token
     "Token", "TokenPayload",
+    # Tree
     "TreeCreate", "TreeUpdate", "TreeResponse", "TreeListResponse",
-    "SessionCreate", "SessionUpdate", "SessionResponse", "SessionExport", "DecisionRecord"
+    # Session
+    "SessionCreate", "SessionUpdate", "SessionResponse", "SessionExport", "DecisionRecord",
+    # Category
+    "CategoryCreate", "CategoryUpdate", "CategoryResponse", "CategoryListResponse",
+    # Tag
+    "TagCreate", "TagResponse", "TagListResponse", "TagAssignment",
+    # Folder
+    "FolderCreate", "FolderUpdate", "FolderResponse", "FolderListResponse", "FolderReorderRequest", "FolderTreeRequest",
 ]