feat: add platform marketing homepage with signup flow

Implement complete marketing homepage for Wizamart targeting Letzshop
vendors in Luxembourg. Includes:

- Marketing homepage with hero, pricing tiers, and add-ons
- 4-step signup wizard with Stripe card collection (30-day trial)
- Letzshop vendor lookup for shop claiming
- Platform API endpoints for pricing, vendors, and signup
- Stripe SetupIntent integration for trial with card upfront
- Database fields for Letzshop vendor identity tracking

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/stripe_service.py

@@ -442,6 +442,118 @@ class StripeService:
             logger.error(f"Webhook signature verification failed: {e}")
             raise ValueError("Invalid webhook signature")
 
+    # =========================================================================
+    # SetupIntent & Payment Method Management
+    # =========================================================================
+
+    def create_setup_intent(
+        self,
+        customer_id: str,
+        metadata: dict | None = None,
+    ) -> stripe.SetupIntent:
+        """
+        Create a SetupIntent to collect card without charging.
+
+        Used for trial signups where we collect card upfront
+        but don't charge until trial ends.
+
+        Args:
+            customer_id: Stripe customer ID
+            metadata: Optional metadata to attach
+
+        Returns:
+            Stripe SetupIntent object with client_secret for frontend
+        """
+        if not self.is_configured:
+            raise ValueError("Stripe is not configured")
+
+        setup_intent = stripe.SetupIntent.create(
+            customer=customer_id,
+            payment_method_types=["card"],
+            metadata=metadata or {},
+        )
+
+        logger.info(f"Created SetupIntent {setup_intent.id} for customer {customer_id}")
+        return setup_intent
+
+    def attach_payment_method_to_customer(
+        self,
+        customer_id: str,
+        payment_method_id: str,
+        set_as_default: bool = True,
+    ) -> None:
+        """
+        Attach a payment method to customer and optionally set as default.
+
+        Args:
+            customer_id: Stripe customer ID
+            payment_method_id: Payment method ID from confirmed SetupIntent
+            set_as_default: Whether to set as default payment method
+        """
+        if not self.is_configured:
+            raise ValueError("Stripe is not configured")
+
+        # Attach the payment method to the customer
+        stripe.PaymentMethod.attach(payment_method_id, customer=customer_id)
+
+        if set_as_default:
+            stripe.Customer.modify(
+                customer_id,
+                invoice_settings={"default_payment_method": payment_method_id},
+            )
+
+        logger.info(
+            f"Attached payment method {payment_method_id} to customer {customer_id} "
+            f"(default={set_as_default})"
+        )
+
+    def create_subscription_with_trial(
+        self,
+        customer_id: str,
+        price_id: str,
+        trial_days: int = 30,
+        metadata: dict | None = None,
+    ) -> stripe.Subscription:
+        """
+        Create subscription with trial period.
+
+        Customer must have a default payment method attached.
+        Card will be charged automatically after trial ends.
+
+        Args:
+            customer_id: Stripe customer ID (must have default payment method)
+            price_id: Stripe price ID for the subscription tier
+            trial_days: Number of trial days (default 30)
+            metadata: Optional metadata to attach
+
+        Returns:
+            Stripe Subscription object
+        """
+        if not self.is_configured:
+            raise ValueError("Stripe is not configured")
+
+        subscription = stripe.Subscription.create(
+            customer=customer_id,
+            items=[{"price": price_id}],
+            trial_period_days=trial_days,
+            metadata=metadata or {},
+            # Use default payment method for future charges
+            default_payment_method=None,  # Uses customer's default
+        )
+
+        logger.info(
+            f"Created subscription {subscription.id} with {trial_days}-day trial "
+            f"for customer {customer_id}"
+        )
+        return subscription
+
+    def get_setup_intent(self, setup_intent_id: str) -> stripe.SetupIntent:
+        """Get a SetupIntent by ID."""
+        if not self.is_configured:
+            raise ValueError("Stripe is not configured")
+
+        return stripe.SetupIntent.retrieve(setup_intent_id)
+
     # =========================================================================
     # Price/Product Management
     # =========================================================================