chore(deps): bump postgres from 17 to 18 in the compose-images group

[dependabot]

Bumps the compose-images group with 1 update: postgres.

Updates postgres from 17 to 18

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[icebergai-review-bot]

IcebergAutoReview

Verdict: request_changes

The PostgreSQL 18 major upgrade is incomplete and can prevent Compose deployments from starting or persisting data correctly.

Findings

• Blocking — docker-compose.yml still mounts iceberg-pg-data at /var/lib/postgresql/data. PostgreSQL 18 changed PGDATA to /var/lib/postgresql/18/docker and requires the volume at /var/lib/postgresql; the official entrypoint detects the old mount and can reject startup. Existing PostgreSQL 17 clusters also require an explicit pg_upgrade or dump/restore migration, which this PR neither implements nor documents. Update the mount, provide a safe upgrade procedure, and add a persistence/startup regression check. Official guidance: https://github.com/docker-library/docs/blob/master/postgres/README.md#pgdata

Validation

• Inspected the complete main...HEAD diff and commit ancestry; only the Compose image tag changed.
• Reviewed Compose volume configuration, backup documentation, PostgreSQL CI services, and focused Compose configuration test.
• Verified from the official PostgreSQL image documentation and image metadata that PostgreSQL 18 uses PGDATA=/var/lib/postgresql/18/docker and VOLUME /var/lib/postgresql.
• Attempted a local image inspection, but Docker is not installed in the review environment; no container was pulled or started.

Residual risks / optional notes

• PR CI does not exercise PostgreSQL 18: both PostgreSQL smoke services remain on version 17, and the Docker/Compose-related jobs are skipped for pull requests.
• README architecture diagrams still describe postgres:17 and the obsolete /var/lib/postgresql/data volume layout.

Automated review by Codex 3f1a5ed4c0c4 using IcebergAutoReview.