Add partial LED side coverage (edge spans) for calibration

Allow LEDs to cover only a fraction of each screen edge via draggable
span bars in the calibration UI. Per-edge start/end (0.0-1.0) values
control which portion of the screen border is sampled for LED colors.

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

server/src/wled_controller/static/style.css

@@ -519,10 +519,15 @@ section {
 
 .layout-index-label {
     position: absolute;
-    bottom: 4px;
+    bottom: 6px;
     left: 6px;
-    font-size: 0.7rem;
-    color: var(--text-secondary);
+    font-size: 0.85rem;
+    font-weight: 600;
+    color: var(--text-color);
+    background: rgba(0, 0, 0, 0.4);
+    padding: 1px 6px;
+    border-radius: 4px;
+    letter-spacing: 0.5px;
 }
 
 .layout-display-label {
@@ -546,11 +551,12 @@ section {
 
 .primary-indicator {
     position: absolute;
-    top: 5px;
-    right: 5px;
+    top: 2px;
+    right: 4px;
     color: var(--primary-color);
-    font-size: 1.2rem;
-    text-shadow: 0 0 3px rgba(0, 0, 0, 0.3);
+    font-size: 1.5rem;
+    line-height: 1;
+    text-shadow: 0 0 4px rgba(0, 0, 0, 0.4);
 }
 
 .layout-legend {
@@ -1084,6 +1090,98 @@ input:-webkit-autofill:focus {
     -moz-appearance: textfield;
 }
 
+/* Edge span bars */
+.edge-span-bar {
+    position: absolute;
+    background: rgba(76, 175, 80, 0.3);
+    border: 1px solid rgba(76, 175, 80, 0.5);
+    border-radius: 3px;
+    cursor: grab;
+    z-index: 1;
+    transition: background 0.15s;
+}
+
+.edge-span-bar:hover {
+    background: rgba(76, 175, 80, 0.45);
+}
+
+.edge-span-bar:active {
+    cursor: grabbing;
+}
+
+/* Horizontal edges: bar spans left-right */
+.edge-top .edge-span-bar,
+.edge-bottom .edge-span-bar {
+    top: 2px;
+    bottom: 2px;
+}
+
+/* Vertical edges: bar spans top-bottom */
+.edge-left .edge-span-bar,
+.edge-right .edge-span-bar {
+    left: 2px;
+    right: 2px;
+}
+
+/* Resize handles */
+.edge-span-handle {
+    position: absolute;
+    background: rgba(255, 255, 255, 0.7);
+    border: 1px solid rgba(76, 175, 80, 0.7);
+    border-radius: 2px;
+    z-index: 2;
+    opacity: 0;
+    transition: opacity 0.15s;
+}
+
+.edge-span-bar:hover .edge-span-handle {
+    opacity: 1;
+}
+
+/* Horizontal handles */
+.edge-top .edge-span-handle,
+.edge-bottom .edge-span-handle {
+    top: 2px;
+    bottom: 2px;
+    width: 6px;
+    cursor: ew-resize;
+}
+
+.edge-top .edge-span-handle-start,
+.edge-bottom .edge-span-handle-start {
+    left: 0;
+}
+
+.edge-top .edge-span-handle-end,
+.edge-bottom .edge-span-handle-end {
+    right: 0;
+}
+
+/* Vertical handles */
+.edge-left .edge-span-handle,
+.edge-right .edge-span-handle {
+    left: 2px;
+    right: 2px;
+    height: 6px;
+    cursor: ns-resize;
+}
+
+.edge-left .edge-span-handle-start,
+.edge-right .edge-span-handle-start {
+    top: 0;
+}
+
+.edge-left .edge-span-handle-end,
+.edge-right .edge-span-handle-end {
+    bottom: 0;
+}
+
+/* Ensure LED input is above span bar */
+.edge-led-input {
+    position: relative;
+    z-index: 2;
+}
+
 /* Corner start-position buttons */
 .preview-corner {
     position: absolute;