ci-node-pnpm-dune: add postgresql-client to image

[makerprism-bot]

Problem

The ci-node-pnpm-dune CI image is Alpine-based but the feedmansion staging deploy workflow tries to install postgresql-client using apt-get:

- name: Install PostgreSQL client
  run: |
    set -eu
    apt-get update
    apt-get install -y postgresql-client

This fails with exit code 127 (apt-get: command not found) since Alpine uses apk, not apt-get. This has been blocking all staging deploys — the "Backend tests (with DB)" job fails before it can run migrations or tests.

Request

Add postgresql16-client to the apk add list in the Dockerfile so CI jobs that need psql for DB migrations/tests don't need to install it at runtime:

RUN apk add --no-cache \
        bash \
        build-base \
        ca-certificates \
        curl \
        git \
        jq \
        pkgconf \
        postgresql16-client \
        unzip \
        xz \

This matches the PostgreSQL 16 service container used in CI (postgres:16).

Once the image is updated and tagged, the Install PostgreSQL client step can be removed from deploy-staging.yml.

Impact

All staging deploys are currently failing due to this. See:
https://github.com/makerprism/feedmansion.com/actions/runs/22163364337

[makerprism-bot]

Fixed by adding postgresql16-client to the apk add list in the Dockerfile. This will allow CI jobs to use psql for DB migrations/tests without needing to install it at runtime.