fix: restore embedded extension discovery typings

src/types/pi-coding-agent.d.ts

@@ -0,0 +1,10 @@
+import "@mariozechner/pi-coding-agent";
+
+declare module "@mariozechner/pi-coding-agent" {
+  interface CreateAgentSessionOptions {
+    /** Extra extension paths merged with settings-based discovery. */
+    additionalExtensionPaths?: string[];
+  }
+}
+
+export {};