SA1029: use typed context key instead of string in main_test.go
S1039: remove unnecessary fmt.Sprintf in validation_test.go
SA4023: fix unreachable nil check on concrete error type
SA4006: fix unused variable assignments in stepca_test.go (4 occurrences)
SA4000: fix duplicate expression in ssh_test.go (BEGIN vs END CERTIFICATE)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Close coverage gaps identified by dual-audit (qualitative + quantitative).
New test files for config (0%→98%), router (0%→100%), handler validation,
health, audit, response helpers, webhook notifier (0%→88%), email notifier,
middleware (recovery, rate limiter), domain profile, service nil-safety,
config helpers, issuer bootstrap, and server bootstrap wiring. Expanded
existing tests for ACME (34%→42%), step-ca (42%→52%), F5, SSH, agent
(43%→63%), scheduler (88%→99%), renewal service, and issuerfactory.
All tests pass: go test -short, go vet, go test -race clean.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
shankar0123