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.

package-lock.json

@@ -8,6 +8,9 @@
       "name": "@alkdev/pubsub",
       "version": "0.1.0",
       "license": "MIT OR Apache-2.0",
+      "dependencies": {
+        "@alkdev/typebox": "^0.34.49"
+      },
       "devDependencies": {
         "@types/node": "^22.0.0",
         "@vitest/coverage-v8": "^3.2.4",
@@ -28,6 +31,12 @@
         }
       }
     },
+    "node_modules/@alkdev/typebox": {
+      "version": "0.34.49",
+      "resolved": "https://registry.npmjs.org/@alkdev/typebox/-/typebox-0.34.49.tgz",
+      "integrity": "sha512-hMidpI6GlMgQMlW9KEd8I3ywgewV6mva9iJaDuBfGtgeRAGrB8yyu6T/fHmgmyQineZ8l4/1PdH/VNr3S2er2g==",
+      "license": "MIT"
+    },
     "node_modules/@ampproject/remapping": {
       "version": "2.3.0",
       "resolved": "https://registry.npmjs.org/@ampproject/remapping/-/remapping-2.3.0.tgz",