feat: add Longcat provider and update GLM model version

- Add Longcat provider preset with Flash-Chat model configuration
- Update mainModelPlaceholder from GLM-4.5 to GLM-4.6 in i18n files
- Configure Longcat with max output tokens (6000) and disabled non-essential traffic

src/i18n/locales/en.json

@@ -169,7 +169,7 @@
     "getApiKey": "Get API Key",
     "parameterConfig": "Parameter Config - {{name}} *",
     "mainModel": "Main Model (optional)",
-    "mainModelPlaceholder": "e.g., GLM-4.5",
+    "mainModelPlaceholder": "e.g., GLM-4.6",
     "fastModel": "Fast Model (optional)",
     "fastModelPlaceholder": "e.g., GLM-4.5-Air",
     "modelHint": "💡 Leave blank to use provider's default model",

src/i18n/locales/zh.json

@@ -169,7 +169,7 @@
     "getApiKey": "获取 API Key",
     "parameterConfig": "参数配置 - {{name}} *",
     "mainModel": "主模型 (可选)",
-    "mainModelPlaceholder": "例如: GLM-4.5",
+    "mainModelPlaceholder": "例如: GLM-4.6",
     "fastModel": "快速模型 (可选)",
     "fastModelPlaceholder": "例如: GLM-4.5-Air",
     "modelHint": "💡 留空将使用供应商的默认模型",