Auth: better-auth plugin evaluation (2FA, OTP, magic link, passkey, last-used, stripe)

[jal-co]

• 2FA (better-auth/2fa; UI ref: hextaui two-factor block)
• Email OTP
• Magic link
• Last-login-method indicator
• Passkey
• better-auth Stripe plugin — evaluate vs our hand-rolled Connect integration (we own marketplace logic; plugin may only fit subscriptions)

[jal-co]

Audit update: keep open, but sequence after #12. First complete secure invitation/provider linking; then evaluate 2FA, OTP, magic link, last-used method, passkeys, recovery policy, and Stripe-plugin fit with tests.