feat: implement Projects and Folders API (v2 architecture)

- Add projectService.js with full CRUD + tree operations
- Add folderService.js with hierarchical folder support
- Add projects.js routes: GET/POST/PUT/DELETE /projects, /projects/:id/tree, /projects/:id/documents
- Add folders.js routes: GET/POST/PUT/DELETE /folders, /folders/:id/tree, /folders/:id/documents
- Update documentService.js to support projectId/folderId with backwards compat (libraryId)
- Update routes/index.js to mount new routers
- Maintain backwards compatibility with legacy libraryId
- All endpoints tested and working

src/routes/folders.js

@@ -0,0 +1,138 @@
+/**
+ * SimpleNote Web - Folders Routes
+ * CRUD + tree for folders
+ */
+
+import { Router } from 'express';
+import { authMiddleware } from '../middleware/auth.js';
+import { getFolderService } from '../services/folderService.js';
+import { NotFoundError, ValidationError } from '../utils/errors.js';
+
+const router = Router();
+router.use(authMiddleware);
+
+// GET /folders?projectId=X&parentId=Y - List folders
+router.get('/', async (req, res) => {
+  try {
+    const { projectId, parentId } = req.query;
+    if (!projectId) {
+      throw new ValidationError('projectId query parameter is required');
+    }
+    const folderService = getFolderService();
+    const folders = await folderService.getFolders(projectId, parentId || null);
+    res.json({ folders });
+  } catch (err) {
+    if (err instanceof ValidationError) {
+      return res.status(400).json({ error: err.message, code: err.code });
+    }
+    if (err instanceof NotFoundError) {
+      return res.status(404).json({ error: err.message, code: err.code });
+    }
+    console.error('Error listing folders:', err);
+    res.status(500).json({ error: 'Internal server error', code: 'INTERNAL_ERROR' });
+  }
+});
+
+// POST /folders - Create folder
+router.post('/', async (req, res) => {
+  try {
+    const { name, projectId, parentId } = req.body;
+    if (!name) {
+      throw new ValidationError('name is required');
+    }
+    if (!projectId) {
+      throw new ValidationError('projectId is required');
+    }
+    const folderService = getFolderService();
+    const folder = await folderService.createFolder({ name, projectId, parentId: parentId || null });
+    res.status(201).json(folder);
+  } catch (err) {
+    if (err instanceof ValidationError || err instanceof NotFoundError) {
+      const status = err instanceof ValidationError ? 400 : 404;
+      return res.status(status).json({ error: err.message, code: err.code });
+    }
+    console.error('Error creating folder:', err);
+    res.status(500).json({ error: 'Internal server error', code: 'INTERNAL_ERROR' });
+  }
+});
+
+// GET /folders/:id - Get folder contents
+router.get('/:id', async (req, res) => {
+  try {
+    const folderService = getFolderService();
+    const folder = await folderService.getFolder(req.params.id);
+    res.json(folder);
+  } catch (err) {
+    if (err instanceof NotFoundError) {
+      return res.status(404).json({ error: err.message, code: err.code });
+    }
+    console.error('Error getting folder:', err);
+    res.status(500).json({ error: 'Internal server error', code: 'INTERNAL_ERROR' });
+  }
+});
+
+// PUT /folders/:id - Update folder
+router.put('/:id', async (req, res) => {
+  try {
+    const { name } = req.body;
+    const folderService = getFolderService();
+    const folder = await folderService.updateFolder(req.params.id, { name });
+    res.json(folder);
+  } catch (err) {
+    if (err instanceof NotFoundError) {
+      return res.status(404).json({ error: err.message, code: err.code });
+    }
+    if (err instanceof ValidationError) {
+      return res.status(400).json({ error: err.message, code: err.code });
+    }
+    console.error('Error updating folder:', err);
+    res.status(500).json({ error: 'Internal server error', code: 'INTERNAL_ERROR' });
+  }
+});
+
+// DELETE /folders/:id - Delete folder
+router.delete('/:id', async (req, res) => {
+  try {
+    const folderService = getFolderService();
+    const result = await folderService.deleteFolder(req.params.id);
+    res.json(result);
+  } catch (err) {
+    if (err instanceof NotFoundError) {
+      return res.status(404).json({ error: err.message, code: err.code });
+    }
+    console.error('Error deleting folder:', err);
+    res.status(500).json({ error: 'Internal server error', code: 'INTERNAL_ERROR' });
+  }
+});
+
+// GET /folders/:id/documents - List documents in folder
+router.get('/:id/documents', async (req, res) => {
+  try {
+    const folderService = getFolderService();
+    const result = await folderService.getFolderDocuments(req.params.id);
+    res.json(result);
+  } catch (err) {
+    if (err instanceof NotFoundError) {
+      return res.status(404).json({ error: err.message, code: err.code });
+    }
+    console.error('Error listing folder documents:', err);
+    res.status(500).json({ error: 'Internal server error', code: 'INTERNAL_ERROR' });
+  }
+});
+
+// GET /folders/:id/tree - Get full folder tree
+router.get('/:id/tree', async (req, res) => {
+  try {
+    const folderService = getFolderService();
+    const tree = await folderService.getFolderTree(req.params.id);
+    res.json(tree);
+  } catch (err) {
+    if (err instanceof NotFoundError) {
+      return res.status(404).json({ error: err.message, code: err.code });
+    }
+    console.error('Error getting folder tree:', err);
+    res.status(500).json({ error: 'Internal server error', code: 'INTERNAL_ERROR' });
+  }
+});
+
+export default router;