fix(api): align frontend API client with backend endpoints

- Fix addDocumentTags to use POST /documents/:id/tags (was using PUT)
- Add getDocumentsByTag(tag) -> GET /tags/:tag
- Add getLibraryTree(id) -> GET /libraries/:id/tree
- Add getLibraryDocuments(id) -> GET /libraries/:id/documents
- Add getProjectDocuments(id) -> GET /projects/:id/documents
- Add getFolder(id) -> GET /folders/:id
- Add getFolderDocuments(id) -> GET /folders/:id/documents
- Add getFolderTree(id) -> GET /folders/:id/tree
- Add api-endpoints.md with full API documentation
- Remove duplicate/unused dead code blocks

public/js/api.js

@@ -36,7 +36,7 @@ class ApiClient {
     }
 
     const response = await fetch(`${API_BASE}${path}`, options);
-    
+
     if (!response.ok) {
       const error = await response.json().catch(() => ({ message: 'Request failed' }));
       throw new Error(error.message || `HTTP ${response.status}`);
@@ -50,7 +50,7 @@ class ApiClient {
   put(path, body) { return this.request('PUT', path, body); }
   delete(path) { return this.request('DELETE', path); }
 
-  // Auth
+  // ===== Auth =====
   async login(token) {
     try {
       this.setToken(token);  // Set token BEFORE making request
@@ -62,7 +62,7 @@ class ApiClient {
     }
   }
 
-  // Documents
+  // ===== Documents =====
   getDocuments(params = {}) {
     const query = new URLSearchParams(params).toString();
     return this.get(`/documents${query ? '?' + query : ''}`);
@@ -90,7 +90,25 @@ class ApiClient {
     }).then(r => r.text());
   }
 
-  // Libraries
+  addDocumentTags(documentId, tags) {
+    return this.post(`/documents/${documentId}/tags`, { tags });
+  }
+
+  moveDocumentToFolder(documentId, folderId) {
+    return this.put(`/documents/${documentId}`, { folderId });
+  }
+
+  // ===== Tags =====
+  getTags() {
+    return this.get('/tags');
+  }
+
+  // GET /tags/:tag - get documents by tag
+  getDocumentsByTag(tag) {
+    return this.get(`/tags/${encodeURIComponent(tag)}`);
+  }
+
+  // ===== Libraries =====
   getLibraries() {
     return this.get('/libraries');
   }
@@ -111,12 +129,17 @@ class ApiClient {
     return this.delete(`/libraries/${id}`);
   }
 
-  // Tags
-  getTags() {
-    return this.get('/tags');
+  // GET /libraries/:id/tree
+  getLibraryTree(id) {
+    return this.get(`/libraries/${id}/tree`);
   }
 
-  // ===== PROJECTS =====
+  // GET /libraries/:id/documents
+  getLibraryDocuments(id) {
+    return this.get(`/libraries/${id}/documents`);
+  }
+
+  // ===== Projects =====
   getProjects() {
     return this.get('/projects');
   }
@@ -137,17 +160,27 @@ class ApiClient {
     return this.delete(`/projects/${id}`);
   }
 
+  // GET /projects/:id/tree
   getProjectTree(id) {
     return this.get(`/projects/${id}/tree`);
   }
 
-  // ===== FOLDERS =====
+  // GET /projects/:id/documents
+  getProjectDocuments(id) {
+    return this.get(`/projects/${id}/documents`);
+  }
+
+  // ===== Folders =====
   getFolders(projectId, parentId = null) {
     const params = new URLSearchParams({ projectId });
     if (parentId) params.append('parentId', parentId);
     return this.get(`/folders?${params.toString()}`);
   }
 
+  getFolder(id) {
+    return this.get(`/folders/${id}`);
+  }
+
   createFolder(data) {
     return this.post('/folders', data);
   }
@@ -160,9 +193,14 @@ class ApiClient {
     return this.delete(`/folders/${id}`);
   }
 
-  // ===== Move document to folder =====
-  moveDocumentToFolder(documentId, folderId) {
-    return this.put(`/documents/${documentId}`, { folderId });
+  // GET /folders/:id/documents
+  getFolderDocuments(id) {
+    return this.get(`/folders/${id}/documents`);
+  }
+
+  // GET /folders/:id/tree
+  getFolderTree(id) {
+    return this.get(`/folders/${id}/tree`);
   }
 }