- 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
