Replace display selection dropdowns with visual display picker lightbox

Remove the Displays tab and replace <select> dropdowns in stream and
template test modals with a lightbox overlay showing the spatial display
layout. Clicking a display selects it. Uses percentage-based positioning
so the layout always fits its container.

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

server/src/wled_controller/static/style.css

@@ -487,32 +487,6 @@ section {
 }
 
 /* Display Layout Visualization */
-.display-layout-preview {
-    background: var(--card-bg);
-    border: 1px solid var(--border-color);
-    border-radius: 8px;
-    padding: 20px;
-    margin-bottom: 20px;
-}
-
-.display-layout-preview h3 {
-    margin: 0 0 15px 0;
-    font-size: 1.1rem;
-    color: var(--text-color);
-}
-
-.display-layout-canvas {
-    background: var(--bg-color);
-    border: 2px dashed var(--border-color);
-    border-radius: 8px;
-    padding: 30px;
-    min-height: 280px;
-    display: flex;
-    align-items: center;
-    justify-content: center;
-    overflow: hidden;
-}
-
 .layout-container {
     position: relative;
     background: transparent;
@@ -527,12 +501,10 @@ section {
     align-items: center;
     justify-content: center;
     box-shadow: 0 4px 6px rgba(0, 0, 0, 0.2);
-    transition: transform 0.2s, box-shadow 0.2s;
-    cursor: help;
+    transition: box-shadow 0.2s, border-color 0.2s;
 }
 
 .layout-display:hover {
-    transform: scale(1.05);
     box-shadow: 0 6px 12px rgba(0, 0, 0, 0.3);
     z-index: 10;
 }
@@ -597,39 +569,6 @@ section {
     text-shadow: 0 0 4px rgba(0, 0, 0, 0.4);
 }
 
-.layout-legend {
-    display: flex;
-    gap: 20px;
-    justify-content: center;
-    margin-top: 15px;
-    padding-top: 15px;
-    border-top: 1px solid var(--border-color);
-}
-
-.legend-item {
-    display: flex;
-    align-items: center;
-    gap: 8px;
-    font-size: 0.9rem;
-    color: var(--text-secondary);
-}
-
-.legend-dot {
-    width: 16px;
-    height: 16px;
-    border-radius: 3px;
-    border: 2px solid;
-}
-
-.legend-dot.primary {
-    border-color: var(--primary-color);
-    background: rgba(76, 175, 80, 0.2);
-}
-
-.legend-dot.secondary {
-    border-color: var(--border-color);
-    background: rgba(128, 128, 128, 0.2);
-}
 
 /* Card brightness slider */
 .brightness-control {
@@ -2327,6 +2266,58 @@ input:-webkit-autofill:focus {
     font-weight: 600;
 }
 
+/* Display Picker Lightbox */
+.display-picker-content {
+    max-width: 900px;
+    width: 90%;
+    text-align: center;
+}
+
+.display-picker-title {
+    color: white;
+    font-size: 1.3rem;
+    margin-bottom: 20px;
+    font-weight: 500;
+}
+
+.display-picker-canvas {
+    background: rgba(255, 255, 255, 0.05);
+    border: 2px dashed rgba(255, 255, 255, 0.15);
+    border-radius: 8px;
+    padding: 24px;
+    width: 100%;
+    box-sizing: border-box;
+}
+
+.layout-display-pickable {
+    cursor: pointer !important;
+}
+
+.layout-display-pickable:hover {
+    box-shadow: 0 0 20px rgba(76, 175, 80, 0.4);
+    border-color: var(--primary-color) !important;
+}
+
+/* Display picker button in forms */
+.btn-display-picker {
+    width: 100%;
+    padding: 10px;
+    border: 1px solid var(--border-color);
+    border-radius: 4px;
+    background: var(--bg-color);
+    color: var(--text-color);
+    font-size: 1rem;
+    cursor: pointer;
+    text-align: left;
+    transition: border-color 0.2s, box-shadow 0.2s;
+    font-weight: 400;
+}
+
+.btn-display-picker:hover {
+    border-color: var(--primary-color);
+    box-shadow: 0 0 0 2px rgba(76, 175, 80, 0.15);
+}
+
 /* Responsive adjustments */
 @media (max-width: 768px) {
     .templates-grid {