Remove client directory and move all subdirectories and files up to root.

The client directory is no longer needed since the former backend directory and node express code were removed from the app. There are redundant directories now: node_modules, public, and files: package.json, yarn.lock, etc.

Inspect the client directory and repository root, including node_modules, public, package.json, and yarn.lock, to understand which items are still needed. Move the required contents to the root, remove the obsolete client directory and redundant files or directories, then verify the app structure and package setup remain usable.

Written by the indexing model from the issue text.