infra: add Docker Compose setup for local development

- Configure PostgreSQL 18 and Valkey 9.1 services
- Create multi-stage Dockerfiles for API and Web apps
- Set up pnpm workspace support in container builds
- Configure hot reload via volume mounts for both services
- Add healthchecks for service orchestration
- Support dev/production stage targets (tsx watch vs compiled)

.env.example

@@ -1 +1,5 @@
-DATABASE_URL=postgres://postgres:mypassword@localhost:5432/postgres
+DATABASE_URL=postgres://postgres:mypassword@db-host:5432/postgres
+
+POSTGRES_USER=postgres
+POSTGRES_PASSWORD=postgres
+POSTGRES_DB=databasename