feat: add billing type tracking and cost enhancements

Add AdapterBillingType (api/subscription/unknown) to adapter execution results
so the system can distinguish API-billed vs subscription-billed runs. Enhance
cost service to aggregate subscription vs API run counts and token breakdowns.
Add limit param to heartbeat runs list API and client.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/adapter-utils/src/index.ts

@@ -2,6 +2,7 @@ export type {
   AdapterAgent,
   AdapterRuntime,
   UsageSummary,
+  AdapterBillingType,
   AdapterExecutionResult,
   AdapterInvocationMeta,
   AdapterExecutionContext,