Add test infrastructure for hydrators using node:test

- Add docker-compose.test.yml with isolated PostgreSQL on port 5433
- Add environment variable support for database connection config
- Add test setup utilities and initial user hydrator tests
- Add test and test:watch scripts to package.json

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

express/package.json

@@ -4,7 +4,8 @@
     "description": "",
     "main": "index.js",
     "scripts": {
-        "test": "echo \"Error: no test specified\" && exit 1",
+        "test": "DB_PORT=5433 DB_USER=diachron_test DB_PASSWORD=diachron_test DB_NAME=diachron_test tsx --test 'framework/**/*.{test,spec}.ts'",
+        "test:watch": "DB_PORT=5433 DB_USER=diachron_test DB_PASSWORD=diachron_test DB_NAME=diachron_test tsx --test --watch 'framework/**/*.{test,spec}.ts'",
         "nodemon": "nodemon dist/index.js",
         "kysely-codegen": "kysely-codegen"
     },