test(crypto): speed passphrase store tests

[taigrr]

Summary

• bump the module Go directive to the verified latest Go release, 1.27.1
• update repo docs to match the Go 1.27 build floor
• add an internal test hook to lower age scrypt cost in engine tests while preserving the production default

Verification

• go generate ./...
• go test ./...
• go test -race ./...
• go vet ./...
• go build -o /tmp/ward ./cmd/ward
• gofmt -l .
• staticcheck ./...