refactor(codex): extract template to config with i18n support

**Changes:**
- Create src/config/codexTemplates.ts with getCodexCustomTemplate factory
- Support both Chinese and English templates based on i18n.language
- Remove 70 lines of duplicated template strings from ProviderForm.tsx
- Update both useEffect and handlePresetChange to use template factory
- Clean up unused "Custom (Blank Template)" preset entry

**Benefits:**
- ✅ Eliminates code duplication (35-line template repeated twice)
- ✅ Adds internationalization support for English users
- ✅ Follows project architecture (templates in config/ directory)
- ✅ Improves maintainability (single source of truth)
- ✅ Net reduction: 34 lines (81 additions, 115 deletions)

**Technical Details:**
- Template selection logic: (i18n.language || "zh").startsWith("zh") ? "zh" : "en"
- Templates are identical except for comments language
- Both auth and config are returned as a single CodexTemplate object

Addresses DRY principle violation and architectural concerns identified
in code review.

src/components/providers/forms/ProviderForm.tsx

@@ -21,6 +21,7 @@ import {
 } from "@/config/geminiProviderPresets";
 import { applyTemplateValues } from "@/utils/providerConfigUtils";
 import { mergeProviderMeta } from "@/utils/providerMetaUtils";
+import { getCodexCustomTemplate } from "@/config/codexTemplates";
 import CodexConfigEditor from "./CodexConfigEditor";
 import { CommonConfigEditor } from "./CommonConfigEditor";
 import GeminiConfigEditor from "./GeminiConfigEditor";
@@ -89,7 +90,7 @@ export function ProviderForm({
   initialData,
   showButtons = true,
 }: ProviderFormProps) {
-  const { t } = useTranslation();
+  const { t, i18n } = useTranslation();
   const isEditMode = Boolean(initialData);
 
   const [selectedPresetId, setSelectedPresetId] = useState<string | null>(
@@ -220,6 +221,15 @@ export function ProviderForm({
     [originalHandleCodexConfigChange, debouncedValidate],
   );
 
+  // Codex 新建模式：初始化时自动填充模板（支持国际化）
+  useEffect(() => {
+    if (appId === "codex" && !initialData && selectedPresetId === "custom") {
+      const locale = (i18n.language || "zh").startsWith("zh") ? "zh" : "en";
+      const template = getCodexCustomTemplate(locale);
+      resetCodexConfig(template.auth, template.config);
+    }
+  }, [appId, initialData, selectedPresetId, resetCodexConfig, i18n.language]);
+
   useEffect(() => {
     form.reset(defaultValues);
   }, [defaultValues, form]);
@@ -525,9 +535,11 @@ export function ProviderForm({
       setActivePreset(null);
       form.reset(defaultValues);
 
-      // Codex 自定义模式：重置为空配置
+      // Codex 自定义模式：加载模板（支持国际化）
       if (appId === "codex") {
-        resetCodexConfig({}, "");
+        const locale = (i18n.language || "zh").startsWith("zh") ? "zh" : "en";
+        const template = getCodexCustomTemplate(locale);
+        resetCodexConfig(template.auth, template.config);
       }
       // Gemini 自定义模式：重置为空配置
       if (appId === "gemini") {