Add Team seat drift repair

[espadonne]

Summary

• add site-admin billing debug detection for Stripe/local Team seat quantity drift
• add a site-admin-only repair action that copies Stripe quantity into local licensed seats and audits success
• document the user Actions secrets API routes required by current trunk docs verification

Tests

• GOCACHE=/private/tmp/shithub-go-cache go test ./internal/billing ./internal/billing/stripebilling ./internal/web/handlers/orgs
• GOCACHE=/private/tmp/shithub-go-cache GOLANGCI_LINT_CACHE=/private/tmp/shithub-golangci-cache make ci