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/routes/commands.ts

@@ -0,0 +1,19 @@
+import type { IncomingMessage, ServerResponse } from "node:http";
+import { listSlashCommands } from "../services/slash-commands.ts";
+import type { WebUiContext } from "../types/context.ts";
+import { json } from "../http/request.ts";
+
+export function handleCommandsRoute(
+	req: IncomingMessage,
+	res: ServerResponse,
+	ctx: WebUiContext,
+	pathname: string,
+): boolean {
+	if (req.method === "GET" && pathname === "/api/commands") {
+		void listSlashCommands(ctx.rpc.sendCmd)
+			.then((commands) => json(res, { commands }))
+			.catch((err) => json(res, { error: err.message }, 500));
+		return true;
+	}
+	return false;
+}