refactor: modularize plugin runtime and test hooks

src/plugins/runtime/runtime-events.ts

@@ -0,0 +1,10 @@
+import { onAgentEvent } from "../../infra/agent-events.js";
+import { onSessionTranscriptUpdate } from "../../sessions/transcript-events.js";
+import type { PluginRuntime } from "./types.js";
+
+export function createRuntimeEvents(): PluginRuntime["events"] {
+  return {
+    onAgentEvent,
+    onSessionTranscriptUpdate,
+  };
+}