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/chat-images.ts

@@ -0,0 +1,24 @@
+const ALLOWED_CHAT_IMAGE_MIME = new Set(["image/jpeg", "image/png", "image/gif", "image/webp"]);
+const MAX_CHAT_IMAGES = 8;
+const MAX_CHAT_IMAGE_BYTES = 10 * 1024 * 1024;
+
+export function normalizeChatImages(
+	images: unknown,
+): Array<{ type: "image"; data: string; mimeType: string }> | undefined {
+	if (!Array.isArray(images) || images.length === 0) return undefined;
+	const out: Array<{ type: "image"; data: string; mimeType: string }> = [];
+	for (const raw of images.slice(0, MAX_CHAT_IMAGES)) {
+		if (!raw || typeof raw !== "object") continue;
+		const mimeType = String((raw as { mimeType?: string }).mimeType || "");
+		const data = String((raw as { data?: string }).data || "");
+		if ((raw as { type?: string }).type !== "image" || !ALLOWED_CHAT_IMAGE_MIME.has(mimeType) || !data) {
+			throw new Error(`不支持的图片类型: ${mimeType || "unknown"}`);
+		}
+		const size = Buffer.from(data, "base64").length;
+		if (size > MAX_CHAT_IMAGE_BYTES) {
+			throw new Error(`图片过大（最大 ${Math.round(MAX_CHAT_IMAGE_BYTES / 1024 / 1024)}MB）`);
+		}
+		out.push({ type: "image", mimeType, data });
+	}
+	return out.length ? out : undefined;
+}