StemRoller: desktop stem separator, Android stems player, and server daemons

- stemroller/: PySide6/QML desktop app and player for separating music into stems
- android/: Plex music player that plays per-stem mixes, with Android Auto support,
  a graphic + parametric (Equalizer APO-style) EQ, and offline downloads
- server/: stemserve (serves stems to the app) and stemd (separates the library on
  the server's GPU, with "Stem Now" priority requests)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

stemroller/player/qml/StemPlayer/RGroup.qml

@@ -0,0 +1,30 @@
+import QtQuick
+
+// A ribbon group: its commands, a caption along the bottom, a rule on the right.
+Item {
+    id: g
+    property string title: ""
+    default property alias content: row.data
+    implicitWidth: Math.max(row.implicitWidth, cap.implicitWidth) + 12
+    height: parent ? parent.height : 92
+    Row {
+        id: row
+        x: 6
+        y: 3
+        height: 68
+        spacing: 2
+    }
+    T {
+        id: cap
+        text: g.title
+        font.pixelSize: X.fsSmall
+        color: X.inkSoft
+        anchors.horizontalCenter: parent.horizontalCenter
+        y: parent.height - 18
+    }
+    Rectangle {
+        anchors { right: parent.right; top: parent.top; bottom: parent.bottom; topMargin: 4; bottomMargin: 4 }
+        width: 1
+        color: X.ribbonLine
+    }
+}