v0.3.0 — All Better Auth plugins wired

Major plugin pass — wired the rest of the better-auth ecosystem.

• Last login method— “Last used” badge on the sign-in page.
• Two-factor authentication — TOTP + backup codes, enable/disable in Settings, verify after sign-in.
• Organizations — switcher, members, invitations, custom roles via access control.
• Admin dashboard — users table (ban / impersonate / promote / delete), audit log viewer.
• Billing — Creem checkout, customer portal, current plan card, usage meter with monthly resets.
• Invitations — share-link or email invites; accepted invites grant the inviter usage credits.
• Email harmony — disposable-domain blocking and email normalization.
• Audit logs — non-blocking, PII-masked, 90-day retention.

Breaking: schema migration required — run bun x @better-auth/cli@latest migrate -y.