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/App.tsx

@@ -4,7 +4,12 @@ import { toast } from "sonner";
 import { Plus, Settings } from "lucide-react";
 import type { Provider } from "@/types";
 import { useProvidersQuery } from "@/lib/query";
-import { providersApi, settingsApi, type AppType, type ProviderSwitchEvent } from "@/lib/api";
+import {
+  providersApi,
+  settingsApi,
+  type AppType,
+  type ProviderSwitchEvent,
+} from "@/lib/api";
 import { useProviderActions } from "@/hooks/useProviderActions";
 import { extractErrorMessage } from "@/utils/errorUtils";
 import { AppSwitcher } from "@/components/AppSwitcher";