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/pages/marketing/SignupPage.tsx

@@ -914,24 +914,31 @@ const SignupPage: React.FC = () => {
                 <ArrowRight className="w-4 h-4" />
               </button>
             ) : (
-              <button
-                type="button"
-                onClick={handleSubmit}
-                disabled={isSubmitting}
-                className="flex items-center gap-2 px-6 py-3 bg-brand-600 text-white rounded-xl hover:bg-brand-700 disabled:opacity-50 disabled:cursor-not-allowed transition-colors font-medium"
-              >
-                {isSubmitting ? (
-                  <>
-                    <Loader2 className="w-4 h-4 animate-spin" />
-                    {t('marketing.signup.creating')}
-                  </>
-                ) : (
-                  <>
-                    <CheckCircle className="w-4 h-4" />
-                    {t('marketing.signup.createAccount')}
-                  </>
+              <div className="flex flex-col items-end gap-2">
+                <button
+                  type="button"
+                  onClick={handleSubmit}
+                  disabled={isSubmitting}
+                  className="flex items-center gap-2 px-6 py-3 bg-brand-600 text-white rounded-xl hover:bg-brand-700 disabled:opacity-50 disabled:cursor-not-allowed transition-colors font-medium"
+                >
+                  {isSubmitting ? (
+                    <>
+                      <Loader2 className="w-4 h-4 animate-spin" />
+                      {t('marketing.signup.creating')}
+                    </>
+                  ) : (
+                    <>
+                      <CheckCircle className="w-4 h-4" />
+                      {t('marketing.signup.createAccount')}
+                    </>
+                  )}
+                </button>
+                {isSubmitting && (
+                  <p className="text-sm text-gray-500 dark:text-gray-400 text-right">
+                    {t('marketing.signup.creatingNote')}
+                  </p>
                 )}
-              </button>
+              </div>
             )}
           </div>
         </div>