feat(documents): zod validators for folder CRUD

createFolderSchema, renameFolderSchema, moveFolderSchema,
moveDocumentToFolderSchema. Names: 1–200 chars, non-whitespace.
parentId/folderId nullable to allow root.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/validators/document-folders.ts

@@ -0,0 +1,28 @@
+import { z } from 'zod';
+
+const folderName = z
+  .string()
+  .min(1, 'Folder name is required')
+  .max(200, 'Folder name cannot exceed 200 characters')
+  .refine((s) => s.trim().length > 0, 'Folder name cannot be only whitespace');
+
+export const createFolderSchema = z.object({
+  name: folderName,
+  parentId: z.string().nullable(),
+});
+export type CreateFolderInput = z.infer<typeof createFolderSchema>;
+
+export const renameFolderSchema = z.object({
+  name: folderName,
+});
+export type RenameFolderInput = z.infer<typeof renameFolderSchema>;
+
+export const moveFolderSchema = z.object({
+  parentId: z.string().nullable(),
+});
+export type MoveFolderInput = z.infer<typeof moveFolderSchema>;
+
+export const moveDocumentToFolderSchema = z.object({
+  folderId: z.string().nullable(),
+});
+export type MoveDocumentToFolderInput = z.infer<typeof moveDocumentToFolderSchema>;