chore: Bump examples to use PG18 - BED-8581

[StephenHinck]

The BHE hosted fleet runs entirely on PG18. We are moving to deprecate PG16 support and migrating new deployments to PG18 ahead of that.

Summary by CodeRabbit

• Chores
  • Updated PostgreSQL database from version 16 to version 18 in development and production environments.
  • Modified database storage volume configuration for improved data persistence management.

[coderabbitai]

Walkthrough

PostgreSQL is upgraded from version 16 to 18 across both development and production docker-compose configurations. The persistent storage volume mount path is updated from /var/lib/postgresql/data to /var/lib/postgresql in parallel across both files.

Changes

PostgreSQL Service Configuration

Layer / File(s)	Summary
Postgres version upgrade and volume mount path docker-compose.dev.yml, docker-compose.yml	The app-db service image is upgraded from postgres:16 to postgres:18, and the volume mount target path is changed from /var/lib/postgresql/data to /var/lib/postgresql consistently in both development and production configurations.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~5 minutes

Poem

🐰 From Postgres sixteen, we hop ahead,
To version eighteen, more robust and fed,
New volume paths align both dev and prod,
A gentle upgrade, by the bunny's nod! 🚀

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: upgrading PostgreSQL from version 16 to 18 in the example Docker Compose files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch BED-8581

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docker-compose.dev.yml`:
- Line 47: The volume mount uses ${BH_POSTGRES_VOLUME:-postgres-data} at
/var/lib/postgresql which may not match the image PGDATA; update
docker-compose.dev.yml to explicitly set PGDATA and/or change the volume target
to the image's default (e.g., set environment variable
PGDATA=/var/lib/postgresql/18/docker and mount
${BH_POSTGRES_VOLUME:-postgres-data}:/var/lib/postgresql/18/docker or add a
secondary mount) so data is reused across upgrades, and add a short migration
note in docs explaining how to copy existing data from /var/lib/postgresql (old
volume) into the new PGDATA path (/var/lib/postgresql/18/docker) before starting
the container.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 52040475-0dee-4c07-affc-ec2817b26654

📥 Commits

Reviewing files that changed from the base of the PR and between b11dac7 and 4795b19.

📒 Files selected for processing (2)

• docker-compose.dev.yml
• docker-compose.yml