fix: migrate glm-4-flash to glm-4-flash-250414 (model deprecated by Zhipu)

Zhipu AI has deprecated glm-4-flash, causing 404 errors on all chat requests.
Updated all references:
- config: glm-4-flash → glm-4-flash-250414, added glm-z1-flash
- frontend: defaultModel, conversationStore, ChatArea fallback, ModelsAPI

desktop/src/components/Settings/ModelsAPI.tsx

@@ -188,7 +188,7 @@ export function ModelsAPI() {
   // 表单状态
   const [formData, setFormData] = useState({
     provider: 'zhipu',
-    modelId: 'glm-4-flash',
+    modelId: 'glm-4-flash-250414',
     displayName: '',
     apiKey: '',
     apiProtocol: 'openai' as 'openai' | 'anthropic' | 'custom',
@@ -678,11 +678,11 @@ export function ModelsAPI() {
                   type="text"
                   value={formData.modelId}
                   onChange={(e) => setFormData({ ...formData, modelId: e.target.value })}
-                  placeholder="如：glm-4-flash, glm-4-plus, glm-4.5"
+                  placeholder="如：glm-4-flash-250414, glm-4-plus, glm-4.7"
                   className="w-full px-3 py-2 border border-gray-200 dark:border-gray-600 rounded-lg text-sm bg-white dark:bg-gray-700 text-gray-900 dark:text-white placeholder-gray-400 focus:outline-none focus:ring-2 focus:ring-orange-500"
                 />
                 <p className="text-xs text-gray-400 mt-1">
-                  智谱: glm-4-flash(免费), glm-4-plus, glm-4.5, glm-4.6
+                  智谱: glm-4-flash-250414(免费), glm-4-plus, glm-4.7, glm-z1-flash(免费推理)
                 </p>
               </div>