Closes partially #15 (network-split side of the same incident class).
Running `docker compose -f docker-compose.infra.yml up -d` puts postgres,
redis, clickhouse, langfuse (and the new temporal service) on a fresh
`molecule-monorepo_default` bridge network, while the platform container
lives on `molecule-monorepo-net` (created by the root docker-compose.yml).
Platform then fails DNS on `postgres:5432` and crashes until the
operator manually `docker network connect`s each service.
Declare `molecule-monorepo-net` as the external default network for the
infra compose file so new services join it automatically.
Also adds temporal + temporal-ui services (closes the 'Temporal unavailable'
noise that every agent logs at startup) and exposes the UI on :8233.
Incident: 2026-04-13 — running `up -d temporal` recreated postgres into
the wrong network and took the platform + all 12 workspace agents offline
until networks were manually reconnected.
