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/contracts/index.ts

@@ -19,7 +19,7 @@ export interface ToolDefinition {
 }
 
 /**
- * The metadata that rides an event as AMQP headers (novox/hq ADR 0042). An event's identity and
+ * The metadata that rides an event as message headers (novox/hq ADR 0042). An event's identity and
  * provenance live here, not in the body, so a consumer — or the broker, or an audit tool — reads
  * who/when/what without parsing the payload. An unknown `x-` header is ignored, not refused: an
  * event is observed by parties that need not all understand every header.