fix: UI polish — notification history buttons, CSS test error handling, schedule time picker, empty state labels

- Notification history: replace text buttons with icon buttons, use modal-footer for proper positioning
- CSS test: reject 0-LED picture sources with clear error message, show WS close reason in UI
- Calibration: distribute LEDs by aspect ratio (16:9 default) instead of evenly across edges
- Value source schedule: replace native time input with custom HH:MM picker matching automation style
- Remove "No ... yet" empty state labels from all CardSection instances

server/src/wled_controller/static/css/components.css

@@ -1024,3 +1024,68 @@ textarea:focus-visible {
     width: 18px;
     height: 18px;
 }
+
+/* ── Schedule time picker (value sources) ── */
+.schedule-row {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    margin-bottom: 6px;
+}
+.schedule-time-wrap {
+    display: flex;
+    align-items: center;
+    gap: 2px;
+    background: var(--bg-color);
+    border: 1px solid var(--border-color);
+    border-radius: var(--radius-sm);
+    padding: 2px 6px;
+    transition: border-color var(--duration-fast) ease;
+}
+.schedule-time-wrap:focus-within {
+    border-color: var(--primary-color);
+    box-shadow: 0 0 0 2px rgba(76, 175, 80, 0.15);
+}
+.schedule-time-wrap input[type="number"] {
+    width: 2.4ch;
+    text-align: center;
+    font-size: 1.1rem;
+    font-weight: 600;
+    font-variant-numeric: tabular-nums;
+    font-family: inherit;
+    background: var(--bg-secondary);
+    border: 1px solid transparent;
+    border-radius: var(--radius-sm);
+    color: var(--text-color);
+    padding: 4px 2px;
+    -moz-appearance: textfield;
+    transition: border-color var(--duration-fast) ease,
+                background var(--duration-fast) ease;
+}
+.schedule-time-wrap input[type="number"]::-webkit-inner-spin-button,
+.schedule-time-wrap input[type="number"]::-webkit-outer-spin-button {
+    -webkit-appearance: none;
+    margin: 0;
+}
+.schedule-time-wrap input[type="number"]:focus {
+    outline: none;
+    border-color: var(--primary-color);
+    background: color-mix(in srgb, var(--primary-color) 8%, var(--bg-secondary));
+}
+.schedule-time-colon {
+    font-size: 1.1rem;
+    font-weight: 700;
+    color: var(--text-muted);
+    line-height: 1;
+    padding: 0 1px;
+    user-select: none;
+}
+.schedule-value {
+    flex: 1;
+    min-width: 60px;
+}
+.schedule-value-display {
+    min-width: 2.5ch;
+    text-align: right;
+    font-variant-numeric: tabular-nums;
+}