Prevent stale provider model selections

Validation could leave a previously fetched model list visible after credentials changed or validation failed, and model selection updated before persistence completed. Clear stale models before validation and only reflect selected models after the credential save succeeds.

Constraint: Address review feedback without changing provider discovery scope.

Confidence: high

Scope-risk: narrow

Tested: npm run build

Tested: git diff --check

Author: H-Chris233

openless-all/app/src/i18n/en.ts

@@ -255,6 +255,7 @@ export const en: typeof zhCN = {
       modelsEmpty: 'Credentials are valid, but no models were returned.',
       modelsLoaded: 'Fetched {{count}} models.',
       selectModel: 'Select a model to fill the field above',
+      modelSaved: 'Saved model {{model}}.',
       validateSuccess: 'Credentials are valid. {{count}} models available.',
       providerHttpStatus: 'Provider returned HTTP {{status}}. Check the API key permissions or endpoint.',
       apiKeyMissing: 'API Key is empty.',

openless-all/app/src/i18n/zh-CN.ts

@@ -253,6 +253,7 @@ export const zhCN = {
       modelsEmpty: '鉴权成功，但没有返回可用模型。',
       modelsLoaded: '已拉取 {{count}} 个模型。',
       selectModel: '选择一个模型写入上方字段',
+      modelSaved: '已保存模型 {{model}}。',
       validateSuccess: '鉴权成功，可用模型 {{count}} 个。',
       providerHttpStatus: '供应商接口返回 {{status}}，请检查 API Key 权限或 Endpoint。',
       apiKeyMissing: 'API Key 为空。',

openless-all/app/src/pages/Settings.tsx

@@ -404,6 +404,8 @@ function ProviderTools({ kind, modelAccount, onModelSelected }: { kind: 'llm' |
   };
 
   const validate = async () => {
+    setModels([]);
+    setSelectedModel('');
     setResult('loading', t('settings.providers.validating'));
     try {
       const result = await validateProviderCredentials(kind);
@@ -436,9 +438,15 @@ function ProviderTools({ kind, modelAccount, onModelSelected }: { kind: 'llm' |
   };
 
   const applyModel = async (model: string) => {
-    setSelectedModel(model);
-    await setCredential(modelAccount, model);
-    onModelSelected();
+    setResult('loading', t('common.saving'));
+    try {
+      await setCredential(modelAccount, model);
+      setSelectedModel(model);
+      onModelSelected();
+      setResult('success', t('settings.providers.modelSaved', { model }));
+    } catch (error) {
+      setResult('error', providerErrorMessage(error, t));
+    }
   };
 
   return (
@@ -451,6 +459,7 @@ function ProviderTools({ kind, modelAccount, onModelSelected }: { kind: 'llm' |
             <select
               value={selectedModel}
               onChange={e => applyModel(e.target.value)}
+              disabled={status === 'loading'}
               style={{ ...inputStyle, maxWidth: 220 }}
             >
               <option value="" disabled>{t('settings.providers.selectModel')}</option>