fix(billing): charge Swedish VAT on Stripe subscriptions (#1011)

The subscription price is net (tax_behavior=exclusive in Stripe), so the
Checkout session now enables Stripe Tax and collects what the rate needs:

- automatic_tax: 25% moms for SE customers, reverse charge for EU-B2B with a
  valid VAT number; it carries onto the subscription so renewals and the
  post-trial first charge stay taxed.
- tax_id_collection + billing_address_collection: capture the VAT number and
  address so Stripe issues a compliant momsfaktura.
- customer_update: persist name/address onto the pre-created customer.

BillingActions now shows "199 kr/man exkl. moms" plus the inkl. price.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

components/settings/BillingActions.tsx

@@ -10,14 +10,14 @@ import type { BillingPlan } from '@/lib/stripe/client'
 const PRICE: Record<BillingPlan, { amount: string; suffix: string; sub: string; cta: string }> = {
   monthly: {
     amount: '199 kr',
-    suffix: '/ mån',
-    sub: 'Faktureras månadsvis.',
+    suffix: '/ mån exkl. moms',
+    sub: '248,75 kr/mån inkl. moms. Faktureras månadsvis.',
     cta: 'Aktivera abonnemang: 199 kr/mån',
   },
   yearly: {
     amount: '166 kr',
-    suffix: '/ mån',
-    sub: '1 999 kr/år: du betalar för 10 månader.',
+    suffix: '/ mån exkl. moms',
+    sub: '1 999 kr/år exkl. moms (2 498,75 kr inkl.). Du betalar för 10 månader.',
     cta: 'Aktivera årsabonnemang: 1 999 kr/år',
   },
 }