Traditional system hardening frameworks often rely on opaque compliance checks and lack automated, safe remediation capabilities. To mitigate these deficits, this paper introduces Hardener, a cross-platform, zero-dependency native binary built on the principle of Documentation-as-Code. By embedding executable audit and remediation logic directly within Markdown frontmatter, Hardener replaces cryptic check identifiers with transparent, human-readable documentation that supports automated fixes and atomic rollbacks. To ensure deterministic reliability across a fragmented Linux ecosystem, the framework utilizes an automated, VM-based test harness (KVM, Vagrant, and libvirt) to validate the tool through a rigorous five-step verification loop across multiple major distributions. The result is a unified solution that guarantees absolute operational transparency, automated compliance enforcement, and immediate system recovery.