fix: update default Docker image to ghcr.io/constructive-io/docker/postgres-plus:17

[pyramation]

Summary

Updates the default Docker image in the pgpm docker CLI command to match the image used in CI workflows. The default image changes from pyramation/pgvector:13.3-alpine to ghcr.io/constructive-io/docker/postgres-plus:17.

Changes made in pgpm/cli/src/commands/docker.ts:

• Updated the help text to show the new default image
• Updated the actual default value used when no --image flag is provided

Review & Testing Checklist for Human

• Verify the ghcr.io/constructive-io/docker/postgres-plus:17 image is publicly accessible and pulls correctly
• Test pgpm docker start locally to confirm the container starts and PostgreSQL is accessible
• Consider if the PostgreSQL version upgrade (13 → 17) could impact existing users who rely on the default image

Notes

This aligns the CLI default with the image used in .github/workflows/run-tests.yaml.

Link to Devin run: https://app.devin.ai/sessions/e7054b498dfa4bf2af31efec4bf8a26f
Requested by: Dan Lynch (@pyramation)

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