Add subcription feature 10

STRIPE_TESTING_GUIDE.md

@@ -10,6 +10,48 @@
 7. [Common Issues & Solutions](#common-issues--solutions)
 8. [Production Checklist](#production-checklist)
 
+
+Flow Without 3DS Required
+
+Step 1: POST /start-registration
+├── Create Stripe Customer
+├── Create SetupIntent with confirm=True
+│   └── Stripe checks: "Does this card need 3DS?" → NO
+│   └── SetupIntent status = 'succeeded' immediately
+├── Store state: {customer_id, setup_intent_id, etc.}
+└── Return: {requires_action: false, setup_intent_id}
+
+Step 2: Frontend sees requires_action=false
+└── Immediately calls /complete-registration (no 3DS popup)
+
+Step 3: POST /complete-registration
+├── Verify SetupIntent status = 'succeeded' ✓ (already succeeded)
+├── Create Subscription with verified payment method
+├── Create User, Tenant, etc.
+└── Return: {user, tokens, subscription}
+Flow With 3DS Required
+
+Step 1: POST /start-registration
+├── Create Stripe Customer
+├── Create SetupIntent with confirm=True
+│   └── Stripe checks: "Does this card need 3DS?" → YES
+│   └── SetupIntent status = 'requires_action'
+├── Store state: {customer_id, setup_intent_id, etc.}
+└── Return: {requires_action: true, client_secret}
+
+Step 2: Frontend sees requires_action=true
+├── Shows 3DS popup: stripe.confirmCardSetup(client_secret)
+├── User completes 3DS verification
+└── Calls /complete-registration
+
+Step 3: POST /complete-registration
+├── Verify SetupIntent status = 'succeeded' ✓ (after 3DS)
+├── Create Subscription with verified payment method
+├── Create User, Tenant, etc.
+└── Return: {user, tokens, subscription}
+
+
+
 ---
 
 ## Prerequisites