The mesh's four streams, asserted on every start

Task 1.4. The foundation set only — a seat's streams come at registration
and a module's consumers at assignment, neither of which has happened at
genesis (ADR 0118).

Asserted rather than created: a stream that was deleted, or a mesh raised
from a backup, must converge rather than run without the guarantee its
messages assume.

Two things the definitions have to get right, both tested:
- CONTROL names its subjects instead of taking mesh.control.>, because
  heartbeats live under that prefix and a stream of them competes for
  retention with the messages that matter
- EVENTS filters on the event token, which is why that token exists; a
  filter over a module's whole namespace would persist every tool call

Overlapping filters are refused where the set is written: NATS accepts two
streams matching one subject and stores the message twice under two
retentions, which nothing reports.

Adds nats.go as a dependency; it pulled golang.org/x/* forward. Full suite
green.

go.mod

@@ -1,19 +1,23 @@
 module github.com/novox/mesh-controller
 
-go 1.25.0
+go 1.26.0
 
 require (
 	github.com/jackc/pgx/v5 v5.10.0
 	github.com/rabbitmq/amqp091-go v1.14.0
-	golang.org/x/crypto v0.55.0
+	golang.org/x/crypto v0.57.0
 )
 
 require (
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
-	golang.org/x/net v0.57.0 // indirect
-	golang.org/x/sync v0.22.0 // indirect
-	golang.org/x/sys v0.47.0 // indirect
-	golang.org/x/text v0.41.0 // indirect
+	github.com/klauspost/compress v1.20.0 // indirect
+	github.com/nats-io/nats.go v1.54.0 // indirect
+	github.com/nats-io/nkeys v0.4.16 // indirect
+	github.com/nats-io/nuid v1.0.1 // indirect
+	golang.org/x/net v0.58.0 // indirect
+	golang.org/x/sync v0.23.0 // indirect
+	golang.org/x/sys v0.48.0 // indirect
+	golang.org/x/text v0.42.0 // indirect
 )