E2E: mock Stellar RPC in CI

[aji70]

Description (Backend)

Platform improvement for MyFans (E2E: mock Stellar RPC in CI). Define scope, implement, and verify in CI or docs.

Tasks

• Implement the change in the relevant code paths
• Wire or persist state where the feature touches runtime behavior
• Add tests (unit, integration, and/or contract/UI as appropriate)

Additional Requirements

• Handle stale, disconnected, or invalid states gracefully where applicable
• Follow existing patterns in this repository (linting, modules, security)

Acceptance Criteria

• Behavior is covered by tests and documented where APIs changed
• No regressions in closely related user or API flows