Show the current tailnet next to the bar icon

Adds a label to the left of the mark naming the tailnet the selected
profile belongs to: the second-from-last label of the domain, so
offscale.pastilhas.dev reads "pastilhas" and headscale.pertento.ai reads
"pertento". Taking the second-level domain rather than a fixed index keeps
the distinctive part if a tailnet ever has four labels.

Read from the accounts list the service already polls, so no extra
process runs for it.

BarIconButton is icon-only by design (labelVisible: false, fixedWidth:
slotSize, and its `text` feeds a glyph rather than a label), so the label
could not live inside it — the bar widget is now a Row of label + button,
and its footprint comes from the row.

Coloured with the brand yellow, dimmed by opacity rather than by
darkening when Tailscale is off: Qt.darker on yellow shifts the hue to
olive instead of quietening it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Panel.qml

@@ -329,8 +329,31 @@ Panel {
     headerIndex = 0
   }
 
-  implicitWidth: button.implicitWidth
-  implicitHeight: button.implicitHeight
+  implicitWidth: barContent.implicitWidth
+  implicitHeight: barContent.implicitHeight
+
+  // Short name of the tailnet the selected profile belongs to, shown in the bar
+  // beside the icon. Takes the second-from-last label of the domain, which is
+  // the distinctive part:
+  //
+  //   headscale.pertento.ai   -> pertento
+  //   offscale.pastilhas.dev  -> pastilhas
+  //
+  // Reads from the accounts list the service already polls, so no extra process
+  // runs for this.
+  readonly property string tailnetName: {
+    var list = tailscale.accounts
+    for (var i = 0; i < list.length; i++) {
+      if (list[i].selected !== true) continue
+      var parts = String(list[i].tailnet || "").split(".")
+      var clean = []
+      for (var j = 0; j < parts.length; j++) if (parts[j] !== "") clean.push(parts[j])
+      if (clean.length >= 2) return clean[clean.length - 2]
+      if (clean.length === 1) return clean[0]
+      return ""
+    }
+    return ""
+  }
 
   onOpenedChanged: if (opened) {
     cursorActive = false
@@ -372,9 +395,31 @@ Panel {
     function status(): string { return tailscale.statusText }
   }
 
+  // Tailnet label to the left of the mark. BarIconButton is icon-only by design
+  // (labelVisible: false, fixedWidth: slotSize, and its `text` feeds a glyph
+  // rather than a label), so the name sits beside it in a Row instead.
+  Row {
+    id: barContent
+    anchors.fill: parent
+    spacing: Style.space(4)
+
+    Text {
+      id: tailnetLabel
+      visible: text !== ""
+      text: root.tailnetName
+      // Brand yellow. Dimmed by opacity rather than by darkening the colour
+      // when Tailscale is off — Qt.darker on yellow slides the hue to olive
+      // instead of just quietening it, the same trap as the IP/DNS subtitle.
+      color: root.accent
+      opacity: tailscale.active ? 1.0 : 0.5
+      font.family: root.fontFamily
+      font.pixelSize: Style.bar.iconFont
+      anchors.verticalCenter: parent.verticalCenter
+    }
+
   BarIconButton {
     id: button
-    anchors.fill: parent
+    anchors.verticalCenter: parent.verticalCenter
     bar: root.bar
     // BarIconButton pins its icon Loader to an `opticalCanvas` sized by
     // Style.bar.iconCanvas (16 * fontScale ~= 27px here). Growing iconSize
@@ -403,6 +448,7 @@ Panel {
       else root.toggle()
     }
   }
+  }
 
   KeyboardPanel {
     id: panel