test: add unit tests for internal/axonops API client

[digiserg]

Summary

internal/axonops/ has 0% test coverage across 1046 lines. This is the core I/O boundary — every CRD controller depends on it. Edge cases (malformed JSON, 204 with decode, URL construction with special chars, error classification) are untested directly.

Testing Requirements

Add internal/axonops/client_test.go with httptest-based tests:

• TestNewClient_Validation — empty host/orgID/apiKey rejected
• TestGetMetricAlertRules_Success / _APIError / _MalformedJSON
• TestCreateOrUpdateMetricAlertRule_GeneratesUUID / _Success / _APIError
• TestDeleteMetricAlertRule_Success / _404Tolerated
• TestCreateKafkaTopic_Success / _APIError
• TestDeleteKafkaACL_Success
• TestCreateScheduledSnapshot_Success
• TestDeleteScheduledRepair_QueryParamID
• TestSetAuthHeader_TokenType
• TestAPIError_IsRetryable — 4xx returns false, 5xx returns true

Acceptance Criteria

1. internal/axonops/ coverage > 70%
2. All client methods have at least success + error test
3. go test -race ./internal/axonops/ passes

Priority

P1