fix(mail): unblock ccb mail setup import on config v3

[HamsteRider-m]

Summary

• remove stale RoutingConfig import from mail_tui.wizard
• map wizard setup outputs to v3 config fields (default_provider, target_email)
• add a regression test that imports mail_tui.wizard to prevent startup regressions

Repro

• before: ccb mail setup failed with cannot import name 'RoutingConfig' from mail.config
• after: wizard starts and prompts for provider/email (no import failure)

Test Plan

• pytest -q test/test_mail_setup_wizard_import.py