Share artifact bytes across API and worker

[ppXD]

Summary

• mount one named artifact volume into both API and worker roles in the compose production topology
• mirror the same topology in deploy E2E
• prove the physical invariant with a live worker-write → API-read cross-role probe

Why

The same /var/lib/codespace/artifacts path in two containers is not the same filesystem. Postgres metadata could survive while >8 KiB model-call/patch bytes remained worker-local, causing missing-path supervisor failures and unreadable UI content.

Compatibility

No application, harness, completion, metric, or terminal semantics change. Existing lost bytes cannot be recreated, but new compose writes survive role boundaries and container recreation. Cloud/multi-host storage remains the versioned-driver migration path.

Validation

• both compose files pass docker compose config -q
• deploy E2E script passes bash -n and now asserts cross-role readback