Dim non-related edges and flow dots when a graph node is selected

- Fix CSS specificity: .dimmed now overrides .graph-edge-active opacity/filter
- Add data-from/data-to to flow dot groups so they can be dimmed per-edge
- Dim flow dots on non-chain edges in highlightChain(), restore on clear

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/wled_controller/static/css/graph-editor.css

@@ -516,8 +516,10 @@ html:has(#tab-graph.active) {
     stroke-width: 2.5;
 }
 
-.graph-edge.dimmed {
+.graph-edge.dimmed,
+.graph-edge.dimmed.graph-edge-active {
     opacity: 0.12;
+    filter: none;
 }
 
 /* Nested edges (composite layers, zones) — not drag-editable */