Migrate backend to Lua; bump deps

* Replace the Python backend with a new Lua implementation (add backend/main.lua, remove backend/main.py)
* Set plugin.json backendType to "lua". Bump package version to 2.0.0
* Upgrade Steambrew and dev dependencies (package.json), with the corresponding pnpm-lock.yaml update.
* Include minor frontend updates to static/faceit_stats.css and webkit/index.tsx.
* Removed built plugin from repo.

Author: alowave