feat: robust automatic DB migration for Docker deployments

Backup before migration (pg_dump/SQLite copy), DB connection wait with
retries, idempotent prisma migrate deploy, old backup cleanup (keep 5),
and server refuses to start if migration fails.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/Dockerfile

@@ -41,6 +41,7 @@ ENV NEXT_TELEMETRY_DISABLED=1
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     openssl \
+    postgresql-client \
     && rm -rf /var/lib/apt/lists/*
 
 RUN groupadd --system --gid 1001 nodejs