Act under a lease, keep accounts by order, one writer at composition (hq to-be 45 Phase 2)

Two controllers could both act (issue 204), a reconcile's report could
overtake the apply after it and the digest decided (issue 267), and a grant
could make a second writer of a machine's report.

- The lease (internal/lease, ADR 0229): mesh-controller_lease key `holder`,
  15 s age, renewed every 5 s by compare-and-set; the epoch is the revision
  it was taken at. The gate is the clock (stops 3 s before expiry); a refused
  renewal is a loss and the process exits; a holder that stops gives it back.
  serve takes it before asserting the bus. Epochs kept in the store
  (migration 0068 controller_epoch) as a floor: a bucket raised from nothing
  is compacted past it. Unleased (no epoch, S12 urgent) only when nobody
  holds it and the bus will not let it be written. A shell command acts
  under the holder's epoch, or its own lease when none.
- Declarations carry `epoch` inside the signed envelope, only to a machine
  whose latest account carried a report_sequence (mesh-host #35); would-send
  is composed with the epoch last sent. Allot and the send both pass the gate.
- Reports: contract in internal/link/order.go (epoch, sequence,
  report_sequence, older_than, refused_older). Accounts kept by epoch, then
  sequence, then report sequence; older refused, counted; unordered reports
  keep the digest rule. Plans by compare-and-set on a revision, with epoch.
  Conditions and calls carry the epoch and are not written off the lease.
- S12 and S13 (naming the writer by epoch) watched, D5 run; reset of the
  bucket said. Writers table compiled in and enforced in PermissionsFor; the
  controller no longer publishes mesh.control.>. A contract per consumed
  kind, and the empty-on-error lint over the repository.
- mesh-host pinned to its main with the epoch in the validator (D1 validates
  the envelope as sent).

Needs mesh-host's genesis lock with the lease grant (mesh-host PR) for
TestTheInstallersFirstUserListIsWhatTheControllerWouldCompose.

internal/broker/testdata/composed.conf

@@ -24,7 +24,7 @@ accounts {
     jetstream: enabled
     users = [
       { user: "controller", password: "$2a$11$cccccccccccccccccccccc", permissions: {
-        publish: { allow: ["$JS.ACK.CONTROL.controller.>", "$JS.ACK.EVENTS.controller.>", "$JS.API.>", "$KV.SEAT_MESH_BUILD_MACHINE_cancelled.>", "$KV.SEAT_NODE_BUILD_AGENT_cancelled.>", "$KV.mesh-controller_calls.>", "$KV.mesh-controller_condition-history.>", "$KV.mesh-controller_conditions.>", "$KV.mesh-controller_hand-acts.>", "$SRV.INFO", "_INBOX.enrol.>", "mesh.assignment.>", "mesh.control.>", "mesh.mod.*.tool.>", "mesh.node.>", "mesh.seat.mesh-build-machine.accept.>", "mesh.seat.mesh-build-machine.tool.>", "mesh.seat.mesh-controller.event.applied", "mesh.seat.mesh-controller.event.built-before", "mesh.seat.mesh-controller.event.condition-changed", "mesh.seat.mesh-controller.event.condition-cleared", "mesh.seat.mesh-controller.event.condition-raised", "mesh.seat.mesh-controller.event.doctor-heartbeat", "mesh.seat.mesh-controller.event.refused", "mesh.seat.mesh-controller.event.secret-replaced", "mesh.seat.node-build-agent.accept.>", "mesh.seat.node-build-agent.tool.>", "mesh.seat.node-intrusion-prevention.tool.banned.*"] }
+        publish: { allow: ["$JS.ACK.CONTROL.controller.>", "$JS.ACK.EVENTS.controller.>", "$JS.API.>", "$KV.SEAT_MESH_BUILD_MACHINE_cancelled.>", "$KV.SEAT_NODE_BUILD_AGENT_cancelled.>", "$KV.mesh-controller_calls.>", "$KV.mesh-controller_condition-history.>", "$KV.mesh-controller_conditions.>", "$KV.mesh-controller_hand-acts.>", "$KV.mesh-controller_lease.>", "$SRV.INFO", "_INBOX.enrol.>", "mesh.assignment.>", "mesh.mod.*.tool.>", "mesh.node.>", "mesh.seat.mesh-build-machine.accept.>", "mesh.seat.mesh-build-machine.tool.>", "mesh.seat.mesh-controller.event.applied", "mesh.seat.mesh-controller.event.built-before", "mesh.seat.mesh-controller.event.condition-changed", "mesh.seat.mesh-controller.event.condition-cleared", "mesh.seat.mesh-controller.event.condition-raised", "mesh.seat.mesh-controller.event.doctor-heartbeat", "mesh.seat.mesh-controller.event.refused", "mesh.seat.mesh-controller.event.secret-replaced", "mesh.seat.node-build-agent.accept.>", "mesh.seat.node-build-agent.tool.>", "mesh.seat.node-intrusion-prevention.tool.banned.*"] }
         subscribe: { allow: ["$JS.API.>", "$JS.EVENT.ADVISORY.CONSUMER.DELETED.>", "$JS.EVENT.ADVISORY.CONSUMER.MAX_DELIVERIES.>", "$SRV.INFO", "$SRV.INFO.mesh-controller", "$SRV.INFO.mesh-controller.>", "$SRV.PING", "$SRV.PING.mesh-controller", "$SRV.PING.mesh-controller.>", "$SRV.STATS", "$SRV.STATS.mesh-controller", "$SRV.STATS.mesh-controller.>", "_DELIVER.controller", "_DELIVER.controller.>", "_INBOX.controller.>", "mesh.control.>", "mesh.mod.*.event.provisioner.failing", "mesh.mod.*.event.provisioner.recovered", "mesh.mod.gitea.event.pull.merged", "mesh.mod.mesh-catalog.event.catching-up", "mesh.mod.mesh-catalog.event.upgraded", "mesh.seat.mesh-build-machine.event.built", "mesh.seat.mesh-controller.tool.>", "mesh.seat.node-build-agent.event.built"] }
         allow_responses: { max: 1, ttl: "1m" }
       } }