Allows contact managers to export and import contacts from the Contacts
page while keeping plain agents blocked. The contacts action menu now
mirrors backend permissions for both export and import.
## Closes
- https://linear.app/chatwoot/issue/CW-4438/contact-export-is-broken
## What changed
- Allows Enterprise custom roles with `contact_manage` to pass
`ContactPolicy#export?` and `ContactPolicy#import?`.
- Shows Export and Import to admins and contact managers only.
- Adds Enterprise policy coverage for contact export and import.
## Screenshots
Admin: Export and Import are available.
<img width="3840" height="2160" alt="Admin contact actions with Export
and Import visible"
src="https://github.com/user-attachments/assets/2b2cdaf2-ca8f-470d-be34-31cba68b9dce"
/>
Contact manager: Export and Import are available.
<img width="3840" height="2160" alt="Contact manager contact actions
with Export and Import visible"
src="https://github.com/user-attachments/assets/48fc038b-2e78-4d0c-ba17-a5965641bd88"
/>
Regular agent: Export and Import are hidden.
<img width="3840" height="2160" alt="Regular agent contact actions with
Export and Import hidden"
src="https://github.com/user-attachments/assets/a63b5731-743a-4223-8dab-ce58383067fe"
/>
## How to test
- Sign in as an administrator and open Contacts; the action menu shows
Export and Import.
- Sign in as a custom-role user with `contact_manage`; the action menu
shows Export and Import.
- Sign in as a plain agent; Export and Import are not available and both
APIs remain unauthorized.
