webui: add calibration editor to the V-Scale toolbar

Adds the Cal row (Scale / Offset / Unit / Reset) to #vscale-menu, its
CSS, and the refreshVScaleMenu() / commitCal() logic that wires it to
calTable and the hub via setCalibrationWS.

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

Client/udpstreamer/static/style.css

@@ -386,6 +386,11 @@ input[type=range].trig-range::-webkit-slider-thumb {
 }
 .vstb-close:hover { color:var(--red); }
 .plot-vscale-bar { display:none; }
+.vstb-sep { width:1px; height:16px; background:var(--surface1); flex-shrink:0; }
+.ctx-num-sm { width:70px; }
+.ctx-num-xs { width:46px; }
+#vscale-cal-lbl { color:var(--mauve); font-weight:600; }
+.cal-invalid { border-color:var(--red) !important; }
 
 /* ── Per-plot cursor value readout (in plot card header) ────────── */
 .plot-cursor-ro {