Web UI: a toggle button that is on looks on outside a segmented group

The 3D room's Cables button turned the cables on and off but looked the
same either way: the "on" style was only defined inside .seg-btns.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/rollcall/web/style.css

@@ -244,3 +244,4 @@ svg.floor .rk text { font-size: 9px; fill: var(--fg); pointer-events: none; font
 .cab-m { margin-top: 8px; border-top: 1px solid var(--line); padding-top: 6px; }
 .cab-p { display: grid; grid-template-columns: 58px minmax(0, 1fr) 14px; gap: 6px; font-size: 12px; padding: 1px 0; } .cab-p > span { overflow-wrap: anywhere; }
 .elev .slot.sw { background: var(--hover); border-left: 3px solid var(--accent); padding: 0 6px; font-size: 11px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
+.btn.on { background: var(--accent); border-color: var(--accent); color: var(--accent-fg); } /* a toggle that is on (Cables), outside a segmented group too */