The sdk names no transport

Task 3.7 of novox/hq ADR 0116, and the whole of the sdk's diff for the bus
change. Three comments said AMQP where they meant 'message headers' and 'a
broker client'; the code never spoke it, which is why no module is rebuilt
for any of this (ADR 0039).

src/messaging/index.ts

@@ -25,7 +25,7 @@ export interface Broker {
 /**
  * How a module obtains its broker. The hosting runtime sets this once; module code calls broker()
  * without knowing the concrete binding. Keeping the binding out of the sdk is deliberate — the sdk
- * carries the contract, not a specific AMQP client build.
+ * carries the contract, not a specific broker client build.
  */
 let binding: (() => Broker) | undefined;