Add host posture checks (roadmap v0.8: posture check)

Add `enodia-sentinel posture check` — a config-hygiene audit that finds
the conditions making a host easy to attack, complementing the live
detectors. Checks: SSH root/password/empty-password login (Include-aware,
first-wins sshd resolution), passwordless and group/world-writable
sudoers, world-writable or non-root PATH directories, loose permissions
on sensitive files (/etc/shadow, /etc/passwd, ...), and downgraded
package-signature policy (reusing pkgdb.siglevel_alert).

Findings reuse the Alert type, so they serialize through the existing
JSON/triage pipeline (`posture check --json`). Each check is a pure
evaluator over injected content/stat facts plus a thin system reader, so
the 18 new tests need no root or live /etc. Posture is command-driven and
never runs in the daemon loop, per the v0.8 exit criterion.

SIDs 100040-100047 (classtype host-posture). Sample config and docs
(COMMAND_REFERENCE, OPERATIONS, ROADMAP, SPECIFICATION) updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -26,10 +26,11 @@ work that is bigger than single alerts.
   alert time, process ancestry, sockets, persistence writes, FIM diffs, package
   transactions, and rootcheck findings.
 - Add `enodia-sentinel incident list/show/export`.
-- Add host posture checks:
-  SSH password login, root SSH login, permissive sudoers entries, unexpected
-  enabled services, world-writable PATH components, disabled package signatures,
-  and unsafe systemd unit settings.
+- ✅ Add host posture checks (`enodia-sentinel posture check`):
+  SSH root/password/empty-password login, passwordless and writable sudoers,
+  world-writable PATH components, loose sensitive-file permissions, and disabled
+  package signatures. Still to come: unexpected enabled services and unsafe
+  systemd unit settings.
 - Add a machine-readable `status --json` command for automation.
 - Update the red-team harness so every current detection has a named drill and
   expected `sid`.