Fix settings persistence, streaming stability, and UI polish

- Fix device settings partial update using model_fields_set for true merge
- Add missing interpolation_mode and smoothing to all API responses
- Fix send_pixels race condition when wled_client is None during stop
- Allow LED segments to exceed edge pixel count (float stepping)
- Fix modal scroll lock using position:fixed to prevent layout shift
- Show loading state for brightness slider until real value is fetched
- Remove stream description from stream selector dialog

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

server/src/wled_controller/static/app.js

@@ -47,16 +47,18 @@ const EDGE_TEST_COLORS = {
     left: [255, 255, 0]
 };
 
-// Modal body lock helpers - prevent layout jump when scrollbar disappears
+// Modal body lock helpers — uses position:fixed to freeze scroll without removing scrollbar
 function lockBody() {
-    const scrollbarWidth = window.innerWidth - document.documentElement.clientWidth;
-    document.body.style.paddingRight = scrollbarWidth + 'px';
+    const scrollY = window.scrollY;
+    document.body.style.top = `-${scrollY}px`;
     document.body.classList.add('modal-open');
 }
 
 function unlockBody() {
+    const scrollY = parseInt(document.body.style.top || '0', 10) * -1;
     document.body.classList.remove('modal-open');
-    document.body.style.paddingRight = '';
+    document.body.style.top = '';
+    window.scrollTo(0, scrollY);
 }
 
 // Image lightbox
@@ -764,12 +766,13 @@ function createDeviceCard(device) {
                 </div>
                 ` : ''}
             </div>
-            <div class="brightness-control">
+            <div class="brightness-control${_deviceBrightnessCache[device.id] == null ? ' brightness-loading' : ''}" data-brightness-wrap="${device.id}">
                 <input type="range" class="brightness-slider" min="0" max="255"
-                       value="${_deviceBrightnessCache[device.id] ?? 128}" data-device-brightness="${device.id}"
+                       value="${_deviceBrightnessCache[device.id] ?? 0}" data-device-brightness="${device.id}"
                        oninput="updateBrightnessLabel('${device.id}', this.value)"
                        onchange="saveCardBrightness('${device.id}', this.value)"
-                       title="${_deviceBrightnessCache[device.id] != null ? Math.round(_deviceBrightnessCache[device.id] / 255 * 100) + '%' : '...'}">
+                       title="${_deviceBrightnessCache[device.id] != null ? Math.round(_deviceBrightnessCache[device.id] / 255 * 100) + '%' : '...'}"
+                       ${_deviceBrightnessCache[device.id] == null ? 'disabled' : ''}>
             </div>
             <div class="card-actions">
                 ${isProcessing ? `
@@ -1231,7 +1234,10 @@ async function fetchDeviceBrightness(deviceId) {
         if (slider) {
             slider.value = data.brightness;
             slider.title = Math.round(data.brightness / 255 * 100) + '%';
+            slider.disabled = false;
         }
+        const wrap = document.querySelector(`[data-brightness-wrap="${deviceId}"]`);
+        if (wrap) wrap.classList.remove('brightness-loading');
     } catch (err) {
         // Silently fail — device may be offline
     }
@@ -4279,7 +4285,6 @@ async function updateStreamSelectorInfo(streamId) {
                 <span class="stream-card-prop" title="${t('streams.type')}">${typeIcon} ${typeName}</span>
                 ${propsHtml}
             </div>
-            ${stream.description ? `<div class="template-config" style="opacity:0.7;">${escapeHtml(stream.description)}</div>` : ''}
         `;
         infoPanel.style.display = '';
     } catch {

server/src/wled_controller/static/style.css

@@ -48,7 +48,8 @@ body {
 }
 
 body.modal-open {
-    overflow: hidden;
+    position: fixed;
+    width: 100%;
 }
 
 .container {
@@ -595,6 +596,11 @@ section {
     width: 100%;
 }
 
+.brightness-loading .brightness-slider {
+    opacity: 0.3;
+    pointer-events: none;
+}
+
 .section-header {
     display: flex;
     align-items: center;