Fix backend TypeScript build errors

- Inline tsconfig.base.json settings into backend/tsconfig.json so the
  Docker build (which only copies backend/) can resolve them
- Replace default imports of Node built-ins (crypto, net) with named imports
- Replace default bcrypt import with named imports (compare, hash)
- Switch @fastify/websocket from v8 to v7 (SocketStream API) to match
  Fastify v4 peer dependency; update WebSocket handler signatures accordingly
- Remove obsolete `version` key from docker-compose.yml

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -1,5 +1,3 @@
-version: '3.9'
-
 services:
   postgres:
     image: postgres:16-alpine