fix: 印尼语在未更新i18nData.json的服务器上回退到en而非zh

- onMounted: 若id语言包缺失，自动使用en作为回退（而非显示中文）
- t(): 默认回退语言从zh改为en（英语比中文更通用）

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docutranslate/static/index.html

@@ -1237,7 +1237,7 @@
             };
 
             const t = (k) => {
-                const dict = i18nData.value[currentLang.value] || i18nData.value['zh'] || {};
+                const dict = i18nData.value[currentLang.value] || i18nData.value['en'] || {};
                 return dict[k] || k;
             };
             const capitalize = (s) => s.charAt(0).toUpperCase() + s.slice(1);
@@ -1875,6 +1875,12 @@
                     const res = await fetch("/static/i18nData.json");
                     i18nData.value = await res.json();
 
+                    // Backward compat: ensure id lang pack exists on servers not yet updated
+                    if (!i18nData.value.id) {
+                        console.warn('id language pack missing, using en as fallback');
+                        i18nData.value.id = i18nData.value.en || {};
+                    }
+
                     // Add new missing translations for Mineru Deploy
                     const extraZh = {
                         mineruDeployParseMethodLabel: "解析方法 (Parse Method)",