fix: unify dialog layout and fix content padding issues

- Fix negative margin overflow in all dialog content areas
- Standardize dialog structure with flex-col layout
- Add consistent py-4 spacing to all content areas
- Ensure proper spacing between header, content, and footer

Affected components:
- AddProviderDialog, EditProviderDialog
- McpFormModal, McpPanel
- UsageScriptModal
- SettingsDialog

All dialogs now follow unified layout pattern:
- DialogContent: flex flex-col max-h-[90vh]
- Content area: flex-1 overflow-y-auto px-6 py-4
- No negative margins that cause content overflow

src/components/mcp/McpFormModal.tsx

@@ -22,8 +22,15 @@ import { mcpApi, type AppType } from "@/lib/api";
 import { McpServer, McpServerSpec } from "@/types";
 import { mcpPresets, getMcpPresetWithDescription } from "@/config/mcpPresets";
 import McpWizardModal from "./McpWizardModal";
-import { extractErrorMessage, translateMcpBackendError } from "@/utils/errorUtils";
-import { tomlToMcpServer, extractIdFromToml, mcpServerToToml } from "@/utils/tomlUtils";
+import {
+  extractErrorMessage,
+  translateMcpBackendError,
+} from "@/utils/errorUtils";
+import {
+  tomlToMcpServer,
+  extractIdFromToml,
+  mcpServerToToml,
+} from "@/utils/tomlUtils";
 import { useMcpValidation } from "./useMcpValidation";
 
 interface McpFormModalProps {
@@ -426,7 +433,7 @@ const McpFormModal: React.FC<McpFormModalProps> = ({
           </DialogHeader>
 
           {/* Content - Scrollable */}
-          <div className="flex-1 overflow-y-auto -mx-6 px-6 space-y-4">
+          <div className="flex-1 overflow-y-auto px-6 py-4 space-y-4">
             {/* 预设选择（仅新增时展示） */}
             {!isEditing && (
               <div>

src/components/mcp/McpPanel.tsx

@@ -25,11 +25,7 @@ interface McpPanelProps {
  * MCP 管理面板
  * 采用与主界面一致的设计风格，右上角添加按钮，每个 MCP 占一行
  */
-const McpPanel: React.FC<McpPanelProps> = ({
-  open,
-  onOpenChange,
-  appType,
-}) => {
+const McpPanel: React.FC<McpPanelProps> = ({ open, onOpenChange, appType }) => {
   const { t } = useTranslation();
   const [isFormOpen, setIsFormOpen] = useState(false);
   const [editingId, setEditingId] = useState<string | null>(null);
@@ -142,7 +138,7 @@ const McpPanel: React.FC<McpPanelProps> = ({
           </div>
 
           {/* Content - Scrollable */}
-          <div className="flex-1 overflow-y-auto -mx-6 px-6">
+          <div className="flex-1 overflow-y-auto px-6 py-4">
             {loading ? (
               <div className="text-center py-12 text-gray-500 dark:text-gray-400">
                 {t("mcp.loading")}