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/database.ts

@@ -21,13 +21,13 @@ import type { SessionData, TokenId } from "./auth/types";
 import type { Domain } from "./types";
 import { AuthenticatedUser, type User, type UserId } from "./user";
 
-// Connection configuration
+// Connection configuration (supports environment variable overrides)
 const connectionConfig = {
-    host: "localhost",
-    port: 5432,
-    user: "diachron",
-    password: "diachron",
-    database: "diachron",
+    host: process.env.DB_HOST ?? "localhost",
+    port: Number(process.env.DB_PORT ?? 5432),
+    user: process.env.DB_USER ?? "diachron",
+    password: process.env.DB_PASSWORD ?? "diachron",
+    database: process.env.DB_NAME ?? "diachron",
 };
 
 // Database schema types for Kysely