Add target FPS slider to Capture Settings and remove unused HACS workflow

- Add Target FPS slider (range 10-90) to Capture Settings dialog
- Fix settings PUT to merge with current values instead of resetting defaults
- Update FPS validation range to 10-90 in schema and config
- Remove irrelevant .github/workflows/validate.yml (HACS leftover)

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

server/src/wled_controller/static/style.css

@@ -997,6 +997,24 @@ input:-webkit-autofill:focus {
     font-size: 0.85rem;
 }
 
+.slider-row {
+    display: flex;
+    align-items: center;
+    gap: 12px;
+}
+
+.slider-row input[type="range"] {
+    flex: 1;
+}
+
+.slider-value {
+    min-width: 28px;
+    text-align: center;
+    font-weight: 600;
+    font-size: 0.95rem;
+    color: var(--text-primary);
+}
+
 .error-message {
     background: rgba(244, 67, 54, 0.1);
     border: 1px solid var(--danger-color);