fix(e2e): make postgres fixture compatible with OpenShift

[sjenning]

Summary

Make the e2e PostgreSQL deployment fixture compatible with OpenShift by addressing UID-based filesystem permission issues that occur when OpenShift assigns random UIDs to pods.

Changes

• Add PGDATA env var pointing to a subdirectory (/var/lib/postgresql/data/pgdata) so postgres creates and owns the directory it needs to chmod, bypassing the UID mismatch
• Add uri field to the postgres secret for connection string convenience
• Add postgres-data and postgres-run emptyDir volume mounts for proper filesystem isolation

Testing

• mise run pre-commit passes (rust lint, format, license headers all green)
• E2E tests verified on OpenShift cluster

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

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[TaylorMutch]

/ok to test 72ce6c2