Put compose worker behind an opt-in profile; align dev Postgres with CI

Commit notes

The compose worker service silently competed with `bun run dev:worker` for the same Redis queue jobs whenever `bun run services:up` (documented as infra-only) was run, contradicting the documented dev model where the API and worker run directly with Bun. Gate it behind the `worker` Compose profile so it's opt-in only. Also bump the dev Postgres image from pg15 to pg16 to match CI, and fix the Dockerfile.worker header comment (the "chunk assembly for resumable uploads" feature was removed).