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>

Test/Components/DataSources/UDPStreamer/UDPStreamerTest.cpp

@@ -236,7 +236,7 @@ bool UDPStreamerTest::TestInitialise_AutoMode_Valid() {
     UDPStreamer ds;
     ConfigurationDatabase cdb;
     cdb.Write("Port", 44502u);
-    cdb.Write("PublishingMode", "Auto");
+    cdb.Write("PublishingMode", "Accumulate");
     cdb.Write("MinRefreshRate", 120.0);
     cdb.CreateRelative("Signals");
     cdb.MoveToRoot();
@@ -248,7 +248,7 @@ bool UDPStreamerTest::TestInitialise_AutoMode_MissingRefreshRate() {
     UDPStreamer ds;
     ConfigurationDatabase cdb;
     cdb.Write("Port", 44503u);
-    cdb.Write("PublishingMode", "Auto");
+    cdb.Write("PublishingMode", "Accumulate");
     /* MinRefreshRate intentionally omitted */
     cdb.CreateRelative("Signals");
     cdb.MoveToRoot();