merge: frame label = clickable drag grip

Drop pointer-events:none on .frame-label and add a pointerdown that
fires startDrag(e,'frame',f.id) — gives m a deterministic select-and-
drag grip at the top-left of every frame where devices/cables can't
occlude it.

web/static/main.js

@@ -482,6 +482,7 @@ function renderCanvas() {
     g.append(rect, label);
     gFrames.append(g);
     rect.addEventListener("pointerdown", (e) => startDrag(e, "frame", f.id));
+    label.addEventListener("pointerdown", (e) => startDrag(e, "frame", f.id));
   }
 
   const portsByDevice = new Map();

web/static/style.css

@@ -180,7 +180,7 @@ body {
   fill: var(--accent);
   font-size: 13px;
   font-weight: 600;
-  pointer-events: none;
+  cursor: grab;
 }
 
 /* Stroke + fill come from the device's user-set colour, written as