feat(api): add sandbox delivery contracts

[bjarn]

Summary:

• regenerate PHP resources and type aliases from the current Sending and Team specifications
• add sandbox delivery request and response contracts
• preserve scheduled mail, typed tags, TLS settings, batch idempotency, and all 53 operations

Validation:

• composer format
• php -d memory_limit=512M vendor/bin/phpstan analyse
• composer test (120 passed, 543 assertions)
• PHP resource and type generator tests