Deploy Alloy to Saruman and oracle #88

Only the monitoring host runs Alloy. morpheus reaches Loki over network
syslog rather than an agent, so it has logs and no host metrics; Saruman and
oracle report nothing at all.

Confirmed live: Prometheus has one *-metrics job (prometheus-metrics), and
Loki has two host values (prometheus, morpheus).

config.alloy is written to run unchanged on every host —
LOKI_URL and PROMETHEUS_REMOTE_WRITE_URL come from the environment, and
after the fix in #62 so does ALLOY_HOSTNAME — so this is deployment, not
configuration.

Saruman first: it is the Proxmox host, and it is the machine ADR-0007 wants
to build stacks/lab/ on. Deciding what oracle is for is a separate item.

Note docs/architecture.md:134-135 and docs/hardware.md:33 disagree about
how many agents are running; whichever is right, it should match after this.

Tracked in docs/roadmap.md; filed as an issue so it has a place to be discussed and closed.