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>

tests/unit/document-folders-validators.test.ts

@@ -0,0 +1,42 @@
+import { describe, it, expect } from 'vitest';
+import {
+  createFolderSchema,
+  renameFolderSchema,
+  moveFolderSchema,
+  moveDocumentToFolderSchema,
+} from '@/lib/validators/document-folders';
+
+describe('document-folder validators', () => {
+  it('accepts a valid create payload', () => {
+    expect(createFolderSchema.safeParse({ name: 'Deals', parentId: null }).success).toBe(true);
+    expect(
+      createFolderSchema.safeParse({ name: 'Q1', parentId: 'abc-123' }).success,
+    ).toBe(true);
+  });
+
+  it('rejects empty + over-long names', () => {
+    expect(createFolderSchema.safeParse({ name: '', parentId: null }).success).toBe(false);
+    expect(
+      createFolderSchema.safeParse({ name: 'x'.repeat(201), parentId: null }).success,
+    ).toBe(false);
+  });
+
+  it('rejects whitespace-only names', () => {
+    expect(createFolderSchema.safeParse({ name: '   ', parentId: null }).success).toBe(false);
+  });
+
+  it('rename schema requires only name', () => {
+    expect(renameFolderSchema.safeParse({ name: 'New' }).success).toBe(true);
+    expect(renameFolderSchema.safeParse({ name: '' }).success).toBe(false);
+  });
+
+  it('move schema accepts null parentId', () => {
+    expect(moveFolderSchema.safeParse({ parentId: null }).success).toBe(true);
+    expect(moveFolderSchema.safeParse({ parentId: 'abc' }).success).toBe(true);
+  });
+
+  it('moveDocumentToFolderSchema accepts null folderId', () => {
+    expect(moveDocumentToFolderSchema.safeParse({ folderId: null }).success).toBe(true);
+    expect(moveDocumentToFolderSchema.safeParse({ folderId: 'abc' }).success).toBe(true);
+  });
+});