[Feature] Option to disable or hide migrate options in settings

Description:

## Request

Add a setting to disable or hide the "migrate" options throughout the Comfy Desktop app. Currently, there's no way to hide these options from the UI without manually editing the app.

## Use Case

Some users may want to completely disable the migration UI elements (banners, context menu options, first-use takeover migrate path) to prevent users from accidentally migrating installs or to enforce a specific deployment policy.

## Proposed Implementation

Add a new setting in `settings.json` (similar to `hideCloudFromPicker`) such as:
```json
"disableMigrateOptions": true
```

When enabled, this would:
- Hide the `MigrationBanner` component
- Remove migrate options from `DetailModal` context menus
- Skip the migrate path in the first-use takeover flow
- Optionally show a message explaining why migration is disabled (if the setting exists in config)

## Alternatives Considered

- UI toggle in the Desktop Settings (similar to the Cloud tile hiding feature)
- Disable it entirely via settings.json only