feat(sproutclaw): modularize webui, extensions, and agent config layout

Restructure local extensions into per-feature directories, split WebUI
into backend modules with slash commands and systemd support, and track
prompts/skills under .pi/agent for portable Gitea deployment.

Co-authored-by: Cursor <cursoragent@cursor.com>

.pi/agent/extensions/webui/backend/http/request.ts

@@ -0,0 +1,23 @@
+import type { IncomingMessage, ServerResponse } from "node:http";
+
+export function json(res: ServerResponse, data: unknown, status = 200): void {
+	res.writeHead(status, { "Content-Type": "application/json" });
+	res.end(JSON.stringify(data));
+}
+
+export function readBody(req: IncomingMessage): Promise<Record<string, unknown>> {
+	return new Promise((resolve, reject) => {
+		let body = "";
+		req.on("data", (chunk: Buffer) => {
+			body += chunk.toString();
+		});
+		req.on("end", () => {
+			try {
+				resolve(JSON.parse(body));
+			} catch {
+				reject(new Error("无效 JSON"));
+			}
+		});
+		req.on("error", reject);
+	});
+}