Let Dex Copilot send WhatsApp messages after confirmation

Allow Dex Copilot to prepare and send a WhatsApp message from the user’s connected account after the user reviews the recipient and message.

Current gap: Copilot cannot send a user-requested note through WhatsApp.

Desired outcome:

• Resolve the intended contact without sending when identity is ambiguous.
• Show the exact recipient and message for confirmation before sending.
• Respect connection, permission, delivery, and rate limits.