Add overlay toggle to calibration dialog, fix serial reconnect on edge test

Add a 💡 button in the calibration modal header (CSS mode only) that
toggles the LED overlay visualization. Auto-stops overlay on modal close
if started from the dialog. Checks and reflects current overlay status
on modal open.

Fix serial devices creating a new connection on every edge test toggle,
which triggered Arduino bootloader resets. Now reuses the cached idle
client for all device types.

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

server/src/wled_controller/static/js/features/calibration.js

@@ -9,6 +9,7 @@ import { API_BASE, getHeaders, fetchWithAuth } from '../core/api.js';
 import { showToast } from '../core/ui.js';
 import { Modal } from '../core/modal.js';
 import { closeTutorial, startCalibrationTutorial } from './tutorials.js';
+import { startCSSOverlay, stopCSSOverlay } from './color-strips.js';
 
 /* ── CalibrationModal subclass ────────────────────────────────── */
 
@@ -37,6 +38,11 @@ class CalibrationModal extends Modal {
     onForceClose() {
         closeTutorial();
         if (_isCSS()) {
+            const cssId = document.getElementById('calibration-css-id')?.value;
+            if (_overlayStartedHere && cssId) {
+                stopCSSOverlay(cssId);
+                _overlayStartedHere = false;
+            }
             _clearCSSTestMode();
             document.getElementById('calibration-css-id').value = '';
             const testGroup = document.getElementById('calibration-css-test-group');
@@ -55,6 +61,7 @@ const calibModal = new CalibrationModal();
 
 let _dragRaf = null;
 let _previewRaf = null;
+let _overlayStartedHere = false;
 
 /* ── Helpers ──────────────────────────────────────────────────── */
 
@@ -83,6 +90,50 @@ async function _clearCSSTestMode() {
     }
 }
 
+function _setOverlayBtnActive(active) {
+    const btn = document.getElementById('calibration-overlay-btn');
+    if (!btn) return;
+    if (active) {
+        btn.style.background = 'var(--primary-color)';
+        btn.style.color = 'white';
+    } else {
+        btn.style.background = '';
+        btn.style.color = '';
+    }
+}
+
+async function _checkOverlayStatus(cssId) {
+    try {
+        const resp = await fetchWithAuth(`/color-strip-sources/${cssId}/overlay/status`);
+        if (resp.ok) {
+            const data = await resp.json();
+            _setOverlayBtnActive(data.active);
+        }
+    } catch { /* ignore */ }
+}
+
+export async function toggleCalibrationOverlay() {
+    const cssId = document.getElementById('calibration-css-id')?.value;
+    if (!cssId) return;
+    try {
+        const resp = await fetchWithAuth(`/color-strip-sources/${cssId}/overlay/status`);
+        if (!resp.ok) return;
+        const { active } = await resp.json();
+        if (active) {
+            await stopCSSOverlay(cssId);
+            _setOverlayBtnActive(false);
+            _overlayStartedHere = false;
+        } else {
+            await startCSSOverlay(cssId);
+            _setOverlayBtnActive(true);
+            _overlayStartedHere = true;
+        }
+    } catch (err) {
+        if (err.isAuth) return;
+        console.error('Failed to toggle calibration overlay:', err);
+    }
+}
+
 /* ── Public API (exported names unchanged) ────────────────────── */
 
 export async function showCalibration(deviceId) {
@@ -114,6 +165,8 @@ export async function showCalibration(deviceId) {
         document.getElementById('calibration-device-id').value = device.id;
         document.getElementById('cal-device-led-count-inline').textContent = device.led_count;
         document.getElementById('cal-css-led-count-group').style.display = 'none';
+        document.getElementById('calibration-overlay-btn').style.display = 'none';
+        document.getElementById('calibration-tutorial-btn').style.marginLeft = '';
 
         document.getElementById('cal-start-position').value = calibration.start_position;
         document.getElementById('cal-layout').value = calibration.layout;
@@ -267,6 +320,14 @@ export async function showCSSCalibration(cssId) {
         calibModal.snapshot();
         calibModal.open();
 
+        // Show overlay toggle and check current status
+        _overlayStartedHere = false;
+        const overlayBtn = document.getElementById('calibration-overlay-btn');
+        overlayBtn.style.display = '';
+        document.getElementById('calibration-tutorial-btn').style.marginLeft = '0';
+        _setOverlayBtnActive(false);
+        _checkOverlayStatus(cssId);
+
         initSpanDrag();
         requestAnimationFrame(() => renderCalibrationCanvas());