fix(cms): detach and audit the publish-triggered deploy (systemd-safe)

A CMS publish's background deploy silently never ran under systemd
(naive 'cmd &' child died with the spawning shell; no log, no trace —
the site kept serving stale content). The spawn now uses
setsid+nohup+stdin-null so it survives any parent exit, and writes
deploy_spawned / deploy_exec_exit audit entries so a failed spawn can
never be silent again.

Closes MITHOME-72

content-editor.js

@@ -305,9 +305,21 @@ const server = http.createServer(async (req, res) => {
       // trigger a rebuild. Deploy only the explicitly configured environment;
       // never default to production. Overridable for tests.
       if (outcome.hadChanges) {
+        // WHY setsid+nohup+stdin-null: under systemd the naive `cmd &` child died
+        // together with the spawning shell (observed: the deploy never ran after a
+        // CMS publish, leaving the site on stale content). Full detachment makes it
+        // survive; the audit entries make the spawn observable instead of silent.
         const deployCmd = process.env.CONTENT_EDITOR_DEPLOY_CMD
-          || `cd ../../../ && ./deploy.sh ${CMS_DEPLOY_ENV} > deploy.log 2>&1 &`;
-        exec(deployCmd);
+          || `cd ../../../ && setsid nohup ./deploy.sh ${CMS_DEPLOY_ENV} > deploy.log 2>&1 < /dev/null &`;
+        writeAudit('deploy_spawned', { clientAddress, user: CMS_USER, env: CMS_DEPLOY_ENV });
+        exec(deployCmd, deployError => {
+          writeAudit('deploy_exec_exit', {
+            clientAddress,
+            user: CMS_USER,
+            result: deployError ? 'error' : 'shell_exited',
+            error: deployError ? String(deployError.message).slice(0, 300) : undefined,
+          });
+        });
       }
       res.end(JSON.stringify({ ok: true, output: outcome.output }));
     });