dev: switch to fully containerized Docker Compose workflow

- Replace tmux setup with a full Docker Compose development stack
- Update backend Dockerfile to use `cargo-chef` caching and `supervisord`
- Containerize frontend development server
- Update tests to run in isolated containers
- Remove legacy `papercrate.tmux`

frontend/webpack.config.js

@@ -65,7 +65,7 @@ module.exports = {
     proxy: [
       {
         context: ['/api', '/download'],
-        target: 'http://127.0.0.1:3000',
+        target: process.env.API_PROXY_PASS,
         changeOrigin: true,
         secure: false,
       },