A `MintAgentMatrixAccount` node creates the agent's account on the swarm's
homeserver with the swarm appservice token, stores its token at
`swarm/agents/<agent>/matrix/main`, and reads it back with whoami before
reporting success. It is a root of agent creation, `after_any` into the
deploy, and a five-minute backfill over every agent with a store identity
queues the same node — the shape of the forge-token mint.
The decision reads the stored token back rather than only checking that one
is stored: the swarm and a hive both pin the device `hyperhive-<agent>`, so
each login replaces the other's token. A failed read plans nothing, so an
outage never rotates every agent's token.
`matrixHomeserverUrl` now defaults to the swarm's `chat.` vhost, since the
mint is what consults it.
