feat(ui): hide the Cron toolbar button by default (opt-in via Header Displays)

The Cron button now follows the same opt-in pattern as the Session Manager /
Away Digest / File Viewer buttons: the template ships the btn-cron--hidden
marker class and applyHeaderVisibilitySettings() removes it only when the
per-device showCronButton setting (App Settings -> Display -> Header Displays)
is enabled. Defaults flipped to false in the mobile defaults block and both
?? fallbacks. Cron jobs remain fully functional; only the launcher is opt-in.

Verified in a live browser: fresh profile hides the button + unchecked toggle,
enabling shows it immediately and persists across reload.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/web/public/index.html

@@ -558,7 +558,7 @@
       <div class="toolbar-right">
         <!-- Orchestrator button hidden until feature is ready -->
         <!-- <button class="btn-toolbar btn-sm" onclick="app.toggleOrchestratorPanel()" title="Orchestrator Loop">&#x2699; Orchestrator</button> -->
-        <button class="btn-toolbar btn-sm btn-cron" onclick="app.openCron()" title="Cron Jobs">&#x23F0; Cron</button>
+        <button class="btn-toolbar btn-sm btn-cron btn-cron--hidden" onclick="app.openCron()" title="Cron Jobs">&#x23F0; Cron</button>
         <span class="version-display" id="versionDisplay" title="Codeman version">v0.0.0</span>
       </div>
     </footer>

src/web/public/settings-ui.js

@@ -328,7 +328,7 @@ Object.assign(CodemanApp.prototype, {
     // Session Manager + Away Digest buttons default OFF; Cron button defaults ON.
     document.getElementById('appSettingsShowSessionButton').checked = settings.showSessionButton ?? defaults.showSessionButton ?? false;
     document.getElementById('appSettingsShowAwayDigestButton').checked = settings.showAwayDigestButton ?? defaults.showAwayDigestButton ?? false;
-    document.getElementById('appSettingsShowCronButton').checked = settings.showCronButton ?? defaults.showCronButton ?? true;
+    document.getElementById('appSettingsShowCronButton').checked = settings.showCronButton ?? defaults.showCronButton ?? false;
     // Gesture control lives in the Input section (alongside Local Echo / CJK Input)
     // but is only available when the instance runs with CODEMAN_GESTURE=1 (server sets
     // window.__codemanGestureAvailable). Hide just this item otherwise so the toggle
@@ -1790,7 +1790,7 @@ Object.assign(CodemanApp.prototype, {
         showRedrawButton: false,
         showSessionButton: false,
         showAwayDigestButton: false,
-        showCronButton: true,
+        showCronButton: false,
         // Remote auto-reconnect (COD-108) — on by default
         remoteAutoReconnect: true,
         // Input
@@ -1964,8 +1964,8 @@ Object.assign(CodemanApp.prototype, {
       awayDigestBtn.classList.toggle('btn-away-digest--hidden', !showAwayDigestButton);
     }
 
-    // Cron button (footer toolbar) — shown by default; hide when disabled.
+    // Cron button (footer toolbar) — opt-in, hidden by default. Same marker pattern.
-    const showCronButton = settings.showCronButton ?? defaults.showCronButton ?? true;
+    const showCronButton = settings.showCronButton ?? defaults.showCronButton ?? false;
     const cronBtn = document.querySelector('.btn-cron');
     if (cronBtn) {
       cronBtn.classList.toggle('btn-cron--hidden', !showCronButton);

src/web/public/styles.css

@@ -9569,9 +9569,9 @@ kbd {
   display: none !important;
 }
 
-/* "Cron" footer-toolbar button — shown by default (App Settings → Display can
+/* "Cron" footer-toolbar button — opt-in, hidden by default (enable under App
-   hide it). Toolbar button, not a header icon, so only the hide marker is
+   Settings → Display → Header Displays). Toolbar button, not a header icon, so
-   needed; out-specify any base .btn-toolbar display. */
+   only the hide marker is needed; out-specify any base .btn-toolbar display. */
 .btn-toolbar.btn-cron--hidden {
   display: none !important;
 }