feat: complete Material Design 3 QML branding rework + antergos-lsb-release

Complete rewrite of the Calamares QML branding with a pure Material
Design 3 (Material You) dark theme. No longer KaOS-derived — all QML
written from scratch for Antergos NeXT.

calamares-sidebar.qml:
  — M3 CenterAlignedTopAppBar at 64dp height with #20252B surface
  — Left: 34dp product logo + "Antergos NeXT" wordmark (17dp Medium,
    0.3 letter-spacing)
  — Right: step indicator dots (7dp circles, active 10dp pill #4A9EFF)
  — Bottom: 3dp animated linear progress bar (400ms OutCubic easing)
  — Subtle level-1 drop shadow (4dp radius, rgba(0,0,0,0.4))

calamares-navigation.qml:
  — M3 Navigation Bar at 68dp height
  — Buttons at 42dp height, 21dp pill radius (per M3 Label Large)
  — Sentence case text ("Back", "Next", "Cancel") in Roboto Medium 14px
  — Back: text button with ← arrow, on-surface hover rgba(0.89,0.89,0.90,0.06)
  — Cancel: text button in error #FFB4AB, error hover rgba(1.0,0.71,0.67,0.07)
  — Next: filled pill 120x42dp in primary #4A9EFF, hover #3B8BDE
  — 120ms ColorAnimation on all button backgrounds
  — Inline Unicode arrows (← →) instead of missing SVG icon files

show.qml:
  — Full-bleed background image with 55% dark overlay + vertical
    gradient (top 15% → transparent → bottom 30%)
  — M3 Elevated Card: 460x380dp, 12dp corner (M3 CornerMedium),
    #2B2930 fill (M3 Surface Container High), 32dp content padding
  — Card shadow: 40dp blur, 56 samples, rgba(0,0,0,0.5)
  — Subtle 1px border at rgba(255,255,255,0.04) for edge definition
  — Title: 26dp Roboto Medium #FFFFFF
  — Body: 14dp Roboto Normal #C4C6D0, 1.55 line-height
  — Footer: 12dp Roboto Medium #8E9099 (M3 Outline)
  — 5 slides with auto-advance every 12s
  — Crossfade transition: 100ms out + 160ms in with OutQuad/InQuad
  — Bottom-left: 140dp wordmark logo at 45% opacity
  — Center-bottom: animated dot indicators matching sidebar style

Slider.qml:
  — Crossfade between Dia slides using SequentialAnimation
  — Removed Animator types (Qt6 render-thread safe)
  — Clean Column layout with centered content

Dia.qml:
  — Unchanged data model (title, body, footer, image)

antergos-lsb-release:
  — New package replacing lsb-release with Antergos NeXT branding
  — /etc/lsb-release shows DISTRIB_ID="Antergos"
  — Added to packages.yaml for CI builds

packages/calamares-branding-antergos-next/calamares-sidebar.qml

@@ -1,62 +1,90 @@
 import io.calamares.ui 1.0
 import io.calamares.core 1.0
 
-import QtQuick 2.3
-import QtQuick.Layouts 1.3
+import QtQuick 2.15
+import QtQuick.Layouts 1.15
 import QtQuick.Controls 2.15
+import Qt5Compat.GraphicalEffects
 
 Rectangle {
-    id: sideBar;
-    color: Branding.styleString( Branding.SidebarBackground );
-    height: 48;
-    width: parent.width
+    id: topBar
+    color: "#20252B"
+    height: 64
+    width: parent ? parent.width : 1024
+
+    layer.enabled: true
+    layer.effect: DropShadow {
+        transparentBorder: true
+        radius: 4
+        samples: 8
+        color: Qt.rgba(0, 0, 0, 0.4)
+    }
 
     RowLayout {
-        anchors.fill: parent;
-        spacing: 0;
+        anchors.fill: parent
+        anchors.leftMargin: 20
+        anchors.rightMargin: 20
+        spacing: 14
 
-        Item {
-            Layout.fillHeight: true;
+        Image {
+            id: logo
+            sourceSize.width: 34
+            sourceSize.height: 34
+            fillMode: Image.PreserveAspectFit
+            source: Branding.imagePath(Branding.ProductLogo)
+            Layout.alignment: Qt.AlignVCenter
         }
 
-        Repeater {
-            model: ViewManager
-            Rectangle {
-                Layout.leftMargin: 0;
-                Layout.fillWidth: true;
-                Layout.alignment: Qt.AlignTop;
-                height: 42;
-                radius: 0;
-                color: Branding.styleString( index == ViewManager.currentStepIndex ? Branding.SidebarBackgroundCurrent : Branding.SidebarBackground );
+        Text {
+            text: "Antergos NeXT"
+            color: "#E3E2E6"
+            font {
+                family: "Roboto"
+                weight: Font.Medium
+                pixelSize: 17
+                letterSpacing: 0.3
+            }
+            Layout.alignment: Qt.AlignVCenter
+        }
 
-                Text {
-                    anchors.verticalCenter: parent.verticalCenter;
-                    anchors.horizontalCenter: parent.horizontalCenter
-                    x: parent.x + 12;
-                    color: Branding.styleString( index == ViewManager.currentStepIndex ? Branding.SidebarTextCurrent : Branding.SidebarText );
-                    text: qsTr(display);
-                    font.pointSize : index == ViewManager.currentStepIndex ? 10 : 9
-                }
+        Item { Layout.fillWidth: true }
+
+        Row {
+            spacing: 8
+            Layout.alignment: Qt.AlignVCenter
+
+            Repeater {
+                id: dotRepeater
+                model: ViewManager
 
                 Rectangle {
-                    height: 2
-                    width: 800
-                    anchors.bottom: parent.bottom;
-                    border.color: Branding.styleString(ViewManager.currentStepIndex === index ? Branding.SidebarTextCurrent : (ViewManager.currentStepIndex >= index ? Branding.SidebarTextCurrent : Branding.SidebarBackgroundCurrent))
-                    border.width: 3
-
-                    Image {
-                        source: "pan-up-symbolic.svg"
-                        id: image
-                        anchors.verticalCenter: parent.verticalCenter;
-                        anchors.verticalCenterOffset : -3
-                        x: parent.x + 35;
-                        fillMode: Image.PreserveAspectFit
-                        height: 32
-                        visible: index == ViewManager.currentStepIndex ? true : false
-                    }
+                    width: index === ViewManager.currentStepIndex ? 10 : 7
+                    height: 7
+                    radius: 3.5
+                    color: index === ViewManager.currentStepIndex
+                        ? "#4A9EFF" : "#8E9099"
+                    opacity: index === ViewManager.currentStepIndex ? 1 : 0.35
+                    Behavior on width { NumberAnimation { duration: 200 } }
+                    Behavior on color { ColorAnimation { duration: 200 } }
                 }
             }
         }
     }
+
+    Rectangle {
+        anchors {
+            bottom: parent.bottom
+            left: parent.left
+            right: parent.right
+        }
+        height: 3
+        color: Qt.rgba(0.56, 0.57, 0.60, 0.2)
+
+        Rectangle {
+            height: parent.height
+            width: parent.width * ((ViewManager.currentStepIndex + 1) / Math.max(dotRepeater.count, 1))
+            color: "#4A9EFF"
+            Behavior on width { NumberAnimation { duration: 400; easing.type: Easing.OutCubic } }
+        }
+    }
 }