feat: integrate Pi backend and Pi Web

pi/packages/coding-agent/examples/extensions/hello.ts

@@ -0,0 +1,26 @@
+/**
+ * Hello Tool - Minimal custom tool example
+ */
+
+import { Type } from "@earendil-works/pi-ai";
+import { defineTool, type ExtensionAPI } from "@earendil-works/pi-coding-agent";
+
+const helloTool = defineTool({
+	name: "hello",
+	label: "Hello",
+	description: "A simple greeting tool",
+	parameters: Type.Object({
+		name: Type.String({ description: "Name to greet" }),
+	}),
+
+	async execute(_toolCallId, params, _signal, _onUpdate, _ctx) {
+		return {
+			content: [{ type: "text", text: `Hello, ${params.name}!` }],
+			details: { greeted: params.name },
+		};
+	},
+});
+
+export default function (pi: ExtensionAPI) {
+	pi.registerTool(helloTool);
+}