Move overlay toggle into calibration visual editor, add tutorial step

Place the overlay button inside the preview screen as a pill toggle,
add it as a tutorial step that auto-skips in device calibration mode.
Tutorial engine now skips hidden/missing targets in both directions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/templates/modals/calibration.html

@@ -3,7 +3,6 @@
     <div class="modal-content" style="max-width: 700px;">
         <div class="modal-header">
             <h2 id="calibration-modal-title" data-i18n="calibration.title">📐 LED Calibration</h2>
-            <button id="calibration-overlay-btn" class="tutorial-trigger-btn" onclick="toggleCalibrationOverlay()" data-i18n-title="overlay.button.show" title="Show overlay visualization" style="display:none">&#x1F4A1;</button>
             <button id="calibration-tutorial-btn" class="tutorial-trigger-btn" onclick="startCalibrationTutorial()" data-i18n-title="calibration.tutorial.start" title="Start tutorial">?</button>
             <button class="modal-close-btn" onclick="closeCalibrationModal()" title="Close" data-i18n-aria-label="aria.close">&#x2715;</button>
         </div>
@@ -42,6 +41,9 @@
                             <label for="cal-border-width" data-i18n="calibration.border_width">Border (px):</label>
                             <input type="number" id="cal-border-width" min="1" max="100" value="10">
                         </div>
+                        <button id="calibration-overlay-btn" class="calibration-overlay-toggle" onclick="toggleCalibrationOverlay()" data-i18n-title="overlay.button.show" title="Show overlay visualization" style="display:none">
+                            &#x1F4A1; <span data-i18n="calibration.overlay_toggle">Overlay</span>
+                        </button>
                     </div>
 
                     <!-- Edge bars with span controls and LED count inputs -->