Add call protocol module with streaming support

New sub-path export @alkdev/pubsub/call providing:
- CallEventSchema (TypeBox schemas) for call.requested/responded/part/completed/aborted/error
- PendingRequestMap with call() (request/response) and subscribe() (streaming via Repeater)
- CallError class and CallErrorCode constants
- Scoped topic subscriptions (call.responded:{requestId}) to avoid O(n) fanout
- subscribe() yields call.part events until call.completed or call.error,
  with automatic call.aborted on consumer break

Also adds @alkdev/typebox as runtime dependency and architecture doc.

tsup.config.ts

@@ -4,6 +4,7 @@ export default defineConfig({
   entry: [
     'src/index.ts',
     'src/event-target-redis.ts',
+    'src/call.ts',
   ],
   format: ['esm', 'cjs'],
   dts: true,