Add initial Prisma migration

.codex/project.md

@@ -22,6 +22,7 @@ Build: npm run build
 Audit: npm run audit
 Release check: npm run release:check
 Docker: docker compose up --build
+Database migrate: npm run db:migrate
 ```
 
 ## Stack
@@ -30,6 +31,12 @@ Docker: docker compose up --build
 Next.js App Router, React, TypeScript, Prisma, Postgres, Socket.IO, Docker
 ```
 
+Database setup:
+
+```text
+Prisma migrations live in prisma/migrations and are applied in Docker with prisma migrate deploy.
+```
+
 Package manager:
 
 ```text