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/services/avatars.ts

@@ -0,0 +1,32 @@
+export function normalizeAvatarUrl(value: unknown): string {
+	if (typeof value !== "string") return "";
+	const url = value.trim();
+	if (!url) return "";
+	let parsed: URL;
+	try {
+		parsed = new URL(url);
+	} catch {
+		throw new Error(`无效头像链接: ${url}`);
+	}
+	if (parsed.protocol !== "http:" && parsed.protocol !== "https:") {
+		throw new Error("头像链接仅支持 http 或 https");
+	}
+	return parsed.toString();
+}
+
+export function normalizeConfigKey(key: unknown): string {
+	if (typeof key !== "string") throw new Error("配置键必须是字符串");
+	const trimmed = key.trim();
+	if (!trimmed) throw new Error("配置键不能为空");
+	if (trimmed.length > 128) throw new Error("配置键过长");
+	if (!/^[a-zA-Z][a-zA-Z0-9_.-]*$/.test(trimmed)) {
+		throw new Error("配置键格式无效");
+	}
+	return trimmed;
+}
+
+export function normalizeConfigValue(value: unknown): string {
+	if (typeof value !== "string") throw new Error("配置值必须是字符串");
+	if (value.length > 65536) throw new Error("配置值过长");
+	return value;
+}