fix: defer Hover login until API use

[intel352]

Summary

• defer Hover authentication until a driver actually calls the Hover API
• keep provider initialization focused on config parsing and client construction
• add a regression test that fails if initialization performs network I/O

Verification

• git diff --check
• GOWORK=off go test ./...

This lets already-delegated DNS plans use public NS state without failing on Hover login before read.