Admin tenant approval flow — new accounts require admin approval before sending

Features

• Admin tenant approval flow — new accounts require admin approval before sending
• Visual refresh with dotted gradient background on login and sign-up pages

Fixes

• Fixed approval emails failing when send request wasn't properly recorded
• Fixed duplicate send requests being created for the same email
• Fixed users being unable to manage their own API keys and domains
• Sending now requires a verified domain to prevent unauthorized use