Add comprehensive unit tests for SID API methods

- Add 22 tests for backup operations (export, import, verify)
- Add tests for seed phrase operations (verify, export)
- Add tests for guardian management (add, list, remove, accept, decline)
- Add tests for guardian recovery flow (initiate, approve, status, cancel)
- Add tests for citizenship application
- Add error handling tests for HTTP errors
- Increase zhtp-api-methods coverage from 47.65% to 59.37%
- Increase overall test count from 168 to 190 tests

Author: umwelt