A long-running `services` app kind: declared TCP ports, always-on, placement, durable volumes — a Minecraft network as the proving workload #391

Today an app is an HTTP child process behind the host-routing proxy that sleeps. Some things are the opposite: a Minecraft network (TCP 25565, never asleep, CPU-hungry, a world on disk), a game server, a broker.

Acceptance (split per run):

• [ ] app.yaml declares kind: service with ports, always_on, placement preference (metal/cloud), volumes with a sync cadence
• [ ] the forge runs it without sablier, exposes the port on a public address it owns, and shows it on the board like any app (tick time / latency as signal where the service reports it)
• [ ] proving workload: a Velocity-style lobby on the always-on front plus one backend, world synced to object storage, failover to a cloud body from the last sync

Waits for the spawn design (bodies) and the profit slider's placement lever.