Enhance API error handling, add lastError tracking, and implement admin home template

api/auth/isauth.php

@@ -9,7 +9,20 @@ if (!isset($internal)) {
 require_once API_DIR . "api.php";
 $api = new gbAPI(true, $internal);
 
-$api->answer(200, [
-    "login" => true,
-    "username" => $api->username
-]);
+$auth = $api->checkAuth();
+
+$lastError = $api->returnLastError();
+
+if ($lastError == NULL) {
+    if ($auth) {
+        $api->answer(200, [
+            "login" => true,
+            "username" => $api->username
+        ]);
+    }else{
+        $api->answer(401, [
+            "login" => false,
+            "username" => ""
+        ]);
+    }
+}