feat: Stripe subscriptions, tier-based permissions, dark mode, and UX improvements

- Fix Stripe SDK v14 compatibility (bracket notation for subscription items)
- Fix subscription period dates from subscription items instead of subscription object
- Add tier-based permissions (can_accept_payments, etc.) on tenant signup
- Add stripe_customer_id field to Tenant model
- Add clickable logo on login page (navigates to /)
- Add database setup message during signup wizard
- Add dark mode support for payment settings and Connect onboarding
- Add subscription management endpoints (cancel, reactivate)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/i18n/locales/en.json

@@ -911,6 +911,7 @@
       "back": "Back",
       "next": "Next",
       "creating": "Creating account...",
+      "creatingNote": "We're setting up your database. This may take up to a minute.",
       "createAccount": "Create Account",
       "haveAccount": "Already have an account?",
       "signIn": "Sign in"