Add comprehensive E2E test coverage for subscription lifecycle

[Smartdevs17]

Description

E2E tests are limited, missing critical subscription flows. Expand test coverage for the full subscription lifecycle.

Acceptance Criteria

• E2E test for subscription creation flow
• E2E test for payment processing (success and failure)
• E2E test for plan change with proration
• E2E test for cancellation and win-back
• E2E test for dunning/recovery flow
• E2E test for multi-currency subscriptions

Technical Scope

• e2e/
• .github/workflows/e2e-detox.yml
• Edge: test flakiness, blockchain-dependent test isolation, test data cleanup