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>

backend/tsconfig.json

@@ -1,11 +1,15 @@
 {
-  "extends": "../tsconfig.base.json",
   "compilerOptions": {
     "target": "ES2021",
     "module": "commonjs",
     "lib": ["ES2021"],
     "outDir": "./dist",
     "rootDir": "./src",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
     "declaration": true,
     "sourceMap": true,
     "moduleResolution": "node"