fix(web): avoid gson-2.1 members-wrapped JSON responses; update AGENTS.md

- sendJsonResponse now serializes JsonElement via toString(), since gson-2.1's
  JSON_ELEMENT factory misses JsonObject/JsonArray subclasses and falls back to
  reflection (leaking the internal "members" field into every REST response)
- Document javac full-path requirement, pre-existing compile warnings,
  frontend page data flow, and gson quirks in AGENTS.md

src/org/kne/cloud/network/klalb/web/KLALBWebServer.java

@@ -119,7 +119,15 @@ public class KLALBWebServer {
 
 	private void sendJsonResponse(HttpExchange exchange, int statusCode, Object data) throws IOException {
 		setCorsHeaders(exchange);
-		byte[] bytes = gson.toJson(data).getBytes(StandardCharsets.UTF_8);
+		String json;
+		if (data instanceof JsonElement) {
+			// gson-2.1 的 toJson(Object) 会按运行时类型 JsonObject 反射序列化出内部的 members 字段，
+			// 必须走 JsonElement 重载（或 toString）直接输出 JSON 树
+			json = ((JsonElement) data).toString();
+		} else {
+			json = gson.toJson(data);
+		}
+		byte[] bytes = json.getBytes(StandardCharsets.UTF_8);
 		exchange.getResponseHeaders().set("Content-Type", "application/json; charset=utf-8");
 		exchange.sendResponseHeaders(statusCode, bytes.length);
 		try (OutputStream os = exchange.getResponseBody()) {