Add Stripe embedded onboarding

- Update StripeConnectOnboarding component with embedded flow
- Add new Stripe routes and service methods for embedded onboarding
- Update EarningsStatus and EarningsDashboard to support new flow
- Add required frontend dependencies

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

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

backend/services/stripeService.js

@@ -64,6 +64,22 @@ class StripeService {
     }
   }
 
+  static async createAccountSession(accountId) {
+    try {
+      const accountSession = await stripe.accountSessions.create({
+        account: accountId,
+        components: {
+          account_onboarding: { enabled: true },
+        },
+      });
+
+      return accountSession;
+    } catch (error) {
+      logger.error("Error creating account session", { error: error.message, stack: error.stack });
+      throw error;
+    }
+  }
+
   static async createTransfer({
     amount,
     currency = "usd",