fix(documents): port-scope folder test cleanup + tighten parent-validation message

Code-review followups on 4b31f01:
- beforeEach now scopes the documentFolders cleanup to the test port
  via .where(eq(documentFolders.portId, portId)) so parallel suites
  don't wipe each other's fixtures.
- Cross-port parent guard message changed from "Parent folder not
  found in this port" (read like a 404) to "Invalid parent folder"
  to match the ValidationError type that already maps to 400.

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

src/lib/services/document-folders.service.ts

@@ -88,7 +88,7 @@ export async function createFolder(
     const parent = await db.query.documentFolders.findFirst({
       where: and(eq(documentFolders.id, data.parentId), eq(documentFolders.portId, portId)),
     });
-    if (!parent) throw new ValidationError('Parent folder not found in this port');
+    if (!parent) throw new ValidationError('Invalid parent folder');
   }
 
   try {

tests/integration/document-folders-crud.test.ts

@@ -9,6 +9,8 @@
 
 import { describe, it, expect, beforeAll, beforeEach } from 'vitest';
 
+import { eq } from 'drizzle-orm';
+
 import { db } from '@/lib/db';
 import { documentFolders } from '@/lib/db/schema/documents';
 import { user } from '@/lib/db/schema/users';
@@ -29,7 +31,7 @@ describe('document-folders service · listTree', () => {
   beforeEach(async () => {
     const port = await makePort();
     portId = port.id;
-    await db.delete(documentFolders).execute();
+    await db.delete(documentFolders).where(eq(documentFolders.portId, portId));
   });
 
   it('returns an empty array when no folders exist', async () => {
@@ -64,7 +66,7 @@ describe('document-folders service · createFolder unique-sibling guard', () =>
   beforeEach(async () => {
     const port = await makePort();
     portId = port.id;
-    await db.delete(documentFolders).execute();
+    await db.delete(documentFolders).where(eq(documentFolders.portId, portId));
   });
 
   it('rejects a duplicate sibling name (case-insensitive)', async () => {
@@ -91,6 +93,6 @@ describe('document-folders service · createFolder unique-sibling guard', () =>
     });
     await expect(
       createFolder(portId, TEST_USER_ID, { name: 'Should fail', parentId: otherFolder.id }),
-    ).rejects.toThrow(/not found in this port/i);
+    ).rejects.toThrow(/invalid parent/i);
   });
 });