Update mock API server for V2 testing #97

Overview

The Docker-based mock API needs to support V2 endpoints and signing.

Requirements

• Add /api/v2/account/getAccountStatusAndUrl endpoint
• Add /api/v2/account/login endpoint (flat body format)
• Add /api/v2/account/checkMFACodeAndLogin for MFA testing
• Validate HMAC-SHA1 signing on requests (or at least accept them)
• Support V2 query parameters
• Keep V1 endpoints for backward compat testing