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/sources.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -135,9 +136,33 @@ func (sm *SourceManager) Load(path string) error {
 
 // ParseSourceArg parses "label@host:port" or "host:port".
 func ParseSourceArg(s string) (label, addr string) {
-	s = strings.TrimSpace(s)
-	if idx := strings.Index(s, "@"); idx >= 0 {
-		return strings.TrimSpace(s[:idx]), strings.TrimSpace(s[idx+1:])
-	}
-	return "", s
+	label, addr, _, _ = ParseSourceArgFull(s)
+	return
+}
+
+// ParseSourceArgFull parses "[label@]host:port[/multicastGroup:dataPort]".
+// Examples:
+//
+//	"Streamer@127.0.0.1:44500/239.0.0.1:44503"  → label="Streamer", addr="127.0.0.1:44500", group="239.0.0.1", port=44503
+//	"127.0.0.1:44501"                            → label="", addr="127.0.0.1:44501", group="", port=0
+func ParseSourceArgFull(s string) (label, addr, multicastGroup string, dataPort int) {
+	s = strings.TrimSpace(s)
+	rest := s
+	if idx := strings.Index(s, "@"); idx >= 0 {
+		label = strings.TrimSpace(s[:idx])
+		rest = strings.TrimSpace(s[idx+1:])
+	}
+	if idx := strings.Index(rest, "/"); idx >= 0 {
+		addr = strings.TrimSpace(rest[:idx])
+		mcastPart := strings.TrimSpace(rest[idx+1:])
+		if lastColon := strings.LastIndex(mcastPart, ":"); lastColon >= 0 {
+			multicastGroup = strings.TrimSpace(mcastPart[:lastColon])
+			dataPort, _ = strconv.Atoi(strings.TrimSpace(mcastPart[lastColon+1:]))
+		} else {
+			multicastGroup = mcastPart
+		}
+	} else {
+		addr = rest
+	}
+	return
 }