fix: resolve API inconsistencies found by Mokoto

- Bug 1: No fix needed - frontend already uses PUT for document updates
- Bug 2: Changed folders API to use 'project' param (matches documents)
- Bug 3: GET /folders now works without project filter (lists all folders)

Changes:
- folders.js: Accept 'project' instead of 'projectId', make it optional
- folderService.js: Support listing all folders when projectId is null
- api.js: Updated getFolders() to use 'project' param consistently

src/routes/folders.js

@@ -11,15 +11,12 @@ import { NotFoundError, ValidationError } from '../utils/errors.js';
 const router = Router();
 router.use(authMiddleware);
 
-// GET /folders?projectId=X&parentId=Y - List folders
+// GET /folders?project=X&parentId=Y - List folders (project is optional, matches documents API)
 router.get('/', async (req, res) => {
   try {
-    const { projectId, parentId } = req.query;
-    if (!projectId) {
-      throw new ValidationError('projectId query parameter is required');
-    }
+    const { project, parentId } = req.query;
     const folderService = getFolderService();
-    const folders = await folderService.getFolders(projectId, parentId || null);
+    const folders = await folderService.getFolders(project || null, parentId || null);
     res.json({ folders });
   } catch (err) {
     if (err instanceof ValidationError) {