feat(ui,api): implement multi-select and folder management enhancements

Implements multi-select functionality in the file browser, allowing users to
perform batch actions such as deleting or moving multiple drawings at once.
Adds full CRUD support for folders, including updating folder properties
and reordering folders via a new `sort_order` column in the database.

- feat(ui): add multi-select, batch delete, and batch move in FileBrowser
- feat(api): add endpoints for updating, deleting, and reordering folders
- feat(db): add `sort_order` column and index to `workspace_folders`
- fix(editor): integrate `useHandleLibrary` for better library management
- chore(deps): update excalidraw subproject

internal/postgres/migrations/00003_folder_order.sql

@@ -0,0 +1,2 @@
+ALTER TABLE workspace_folders ADD COLUMN IF NOT EXISTS sort_order INTEGER NOT NULL DEFAULT 0;
+CREATE INDEX IF NOT EXISTS idx_workspace_folders_sort_order ON workspace_folders(team_id, sort_order);