docs(ipc): fix embedded map system example missed by prior sweep

The previous doc sweep rewrote `<code>NAME</code>` and `(NAME `
patterns but missed `(map system ["echo hi"])` — the builtin sat
in a higher-order position inside another bracketed form, so
neither substitution matched.  Rewrites to
`(map .sys.exec ["echo hi"])`, which is both the accurate new
name and the exact expression the restricted-mode test in
test_store.c already exercises.

Author: singaraiona

website/docs/ipc.html

@@ -188,7 +188,7 @@ <h3>-U (password + restricted mode)</h3>
 <span class="hl-comment">;; =&gt; 3  (queries still work)</span></code></pre>
 
       <div class="info-box">
-        <strong>Security note.</strong> Restriction applies to all dispatch paths including higher-order functions. <code>(map system ["echo hi"])</code> is also blocked in restricted mode.
+        <strong>Security note.</strong> Restriction applies to all dispatch paths including higher-order functions. <code>(map .sys.exec ["echo hi"])</code> is also blocked in restricted mode.
       </div>
 
       <h2 id="client-builtins">Client Builtins</h2>