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/qml/StemRoller/Card.qml

@@ -0,0 +1,26 @@
+import QtQuick
+
+// Material card (elevation 2, radius 8) with Aero top gloss: white 6% -> 0 over the top 40%.
+Rectangle {
+    id: card
+    property int elevation: 2
+    property bool glossy: true
+    radius: 8
+    color: Theme.surface1
+    border.color: Theme.hairline
+    border.width: 1
+
+    Elevation { level: card.elevation; radius: card.radius }
+
+    Rectangle {
+        visible: card.glossy
+        anchors { left: parent.left; right: parent.right; top: parent.top; margins: 1 }
+        height: (parent.height - 2) * 0.4
+        topLeftRadius: card.radius - 1
+        topRightRadius: card.radius - 1
+        gradient: Gradient {
+            GradientStop { position: 0; color: Qt.rgba(1, 1, 1, 0.06) }
+            GradientStop { position: 1; color: Qt.rgba(1, 1, 1, 0.0) }
+        }
+    }
+}