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/config/cli.ts

@@ -0,0 +1,9 @@
+export function parsePort(argv: string[] = process.argv.slice(2)): number {
+	const idx = argv.indexOf("--port");
+	const raw = idx !== -1 ? argv[idx + 1] : "19133";
+	const port = parseInt(raw || "19133", 10);
+	if (!Number.isFinite(port) || port < 1 || port > 65535) {
+		throw new Error(`无效端口: ${raw}`);
+	}
+	return port;
+}