feat(sprint-6): Phase 3 — Stripe integration (SEPA + PayPal + Card)

- V7 migration: subscriptions table with plan tiers
- Subscription entity + PlanTier/SubscriptionStatus enums
- StripeService: customer creation, checkout, portal, webhook handling
- SubscriptionController: /api/v1/billing endpoints
- Webhook handler: invoice.paid, payment_failed, subscription.deleted/updated
- Plan enforcement: member limit interceptor, trial expiry check
- Frontend: /settings/billing page (plan card, usage, upgrade, portal link)
- Trial expired banner on all admin pages
- React Query hooks (useSubscriptionQuery, checkout/portal mutations)
- Stripe Java SDK 28.2.0
- Full i18n (de/en) for billing namespace

cannamanage-service/pom.xml

@@ -79,6 +79,12 @@
             <artifactId>commons-csv</artifactId>
             <version>1.12.0</version>
         </dependency>
+        <!-- Stripe Java SDK -->
+        <dependency>
+            <groupId>com.stripe</groupId>
+            <artifactId>stripe-java</artifactId>
+            <version>28.2.0</version>
+        </dependency>
     </dependencies>
 
     <build>