WebUI: per-signal vscale toolbar, active-signal highlighting, zoom fix

- Per-signal, per-plot vertical scale state (sigVScale keyed by plotId:signalKey)
  so the same signal in two plots has fully independent vscale config
- Active signal redrawn on top of all series with 2× line width for clear
  visual identification; badge click toggles selection and opens/closes the
  embedded vscale toolbar (click same badge again to deselect)
- Vscale configurator moved from floating popup to a slim toolbar strip
  anchored inside the plot card, with an × close button
- Trigger dropdown shows one entry per array signal with [0…N-1] label;
  opening it shows an index-picker dialog to choose the element
- Zoom resampling: when server returns no data for a zoomed range, fall
  back to the local circular buffer instead of returning empty arrays

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

Client/WebUI/static/style.css

@@ -311,6 +311,48 @@ input[type=range].trig-range::-webkit-slider-thumb {
 }
 .ctx-range { width:80px; }
 .ctx-range-val { font-size:11px; color:var(--mauve); min-width:26px; }
+.ctx-num {
+  width:90px; background:var(--surface0); border:1px solid var(--surface1); border-radius:4px;
+  color:var(--text); font-size:11px; padding:2px 6px;
+}
+.ctx-num:focus { outline:none; border-color:var(--accent); }
+.ctx-btn:disabled { opacity:0.35; cursor:not-allowed; border-color:var(--surface1); }
+
+/* ── Array index picker ─────────────────────────────────────────── */
+#array-idx-picker {
+  position:fixed; z-index:300;
+  background:var(--mantle); border:1px solid var(--surface1); border-radius:var(--radius);
+  box-shadow:0 8px 24px rgba(0,0,0,0.6); padding:10px; min-width:200px;
+}
+
+/* ── VScale toolbar (embedded in plot card) ──────────────────────── */
+#vscale-menu {
+  flex-shrink:0; background:rgba(17,17,27,0.92); border-top:1px solid var(--surface1);
+  padding:3px 8px;
+}
+.vstb-header {
+  display:flex; align-items:center; gap:8px; flex-wrap:nowrap; overflow-x:auto;
+  scrollbar-width:none;
+}
+.vstb-header::-webkit-scrollbar { display:none; }
+.vstb-label { font-size:11px; color:var(--subtext0); white-space:nowrap; flex-shrink:0; }
+.vstb-lbl { font-size:10px; color:var(--overlay0); white-space:nowrap; }
+.vstb-close {
+  margin-left:auto; flex-shrink:0;
+  background:transparent; border:none; color:var(--overlay0);
+  cursor:pointer; font-size:11px; padding:0 3px; line-height:1;
+  transition:color var(--transition);
+}
+.vstb-close:hover { color:var(--red); }
+.plot-vscale-bar { display:none; }
+
+/* ── Badge vscale info & active state ───────────────────────────── */
+.vscale-info {
+  font-size:9px; color:var(--overlay0); font-family:monospace; margin-left:2px; white-space:nowrap;
+}
+.sig-badge { cursor:pointer; }
+.sig-badge-active { outline:1px solid rgba(255,255,255,0.35); background:rgba(88,91,112,0.9); }
+.sig-badge-active .vscale-info { color:var(--subtext0); }
 
 /* ── Source groups ────────────────────────────────────────────── */
 .source-group { margin-bottom:2px; }