💳 feat(stripe): add SEPA Direct Debit payment option

- Add sepa_debit to payment_method_types for credit purchases
- Add sepa_debit to subscription checkout sessions
- Handle payment_intent.processing webhook for SEPA status tracking
- Add blueprint article analyzing payment options (Stripe vs LSV+/FinTS)

SEPA offers lower fees (0.8% vs 1.5%+€0.25) for DACH customers.
Payments are confirmed 3-14 days after checkout (bank processing).

services/mana-core-auth/src/stripe/stripe-webhook.controller.ts

@@ -69,13 +69,26 @@ export class StripeWebhookController {
 		});
 
 		// Handle relevant events
+		// Note: SEPA Direct Debit payments are not instant - they go through:
+		// 1. checkout.session.completed (payment_status may be 'unpaid' for SEPA)
+		// 2. payment_intent.processing (SEPA is being processed by banks)
+		// 3. payment_intent.succeeded (3-14 days later when bank confirms)
+		// Credits are only added on payment_intent.succeeded for safety.
 		switch (event.type) {
 			// Credit purchases via Checkout Session
 			case 'checkout.session.completed':
 				await this.handleCheckoutSessionCompleted(event.data.object as Stripe.Checkout.Session);
 				break;
 
-			// Credit purchases
+			// Payment processing (SEPA: bank is processing the debit)
+			case 'payment_intent.processing':
+				this.logger.log('Payment processing (SEPA in progress)', {
+					paymentIntentId: (event.data.object as Stripe.PaymentIntent).id,
+				});
+				// Purchase stays in 'pending' status until succeeded
+				break;
+
+			// Credit purchases - payment confirmed
 			case 'payment_intent.succeeded':
 				await this.handlePaymentSucceeded(event.data.object as Stripe.PaymentIntent);
 				break;

services/mana-core-auth/src/stripe/stripe.service.ts

@@ -185,7 +185,7 @@ export class StripeService {
 			const session = await stripe.checkout.sessions.create({
 				customer: options.customerId,
 				mode: 'payment',
-				payment_method_types: ['card'],
+				payment_method_types: ['card', 'sepa_debit'],
 				line_items: [
 					{
 						price_data: {

services/mana-core-auth/src/subscriptions/subscriptions.service.ts

@@ -139,7 +139,7 @@ export class SubscriptionsService {
 		const session = await this.stripe.checkout.sessions.create({
 			customer: stripeCustomerId,
 			mode: 'subscription',
-			payment_method_types: ['card'],
+			payment_method_types: ['card', 'sepa_debit'],
 			line_items: [
 				{
 					price: stripePriceId,