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/Glow.qml

@@ -0,0 +1,18 @@
+import QtQuick
+
+// Static 9-patch Aero hover glow; animate `opacity` only.
+BorderImage {
+    property color color: Theme.accentGlow
+    property int radius: 20
+    property int sigma: 6
+    readonly property int m: Math.ceil(sigma * 3) + 1
+    anchors.fill: parent
+    anchors.margins: -m
+    border { left: m + radius; right: m + radius; top: m + radius; bottom: m + radius }
+    source: "image://fx/glow/" + Theme.hex(color) + "/" + sigma + "/" + radius
+    opacity: 0
+    visible: opacity > 0.001
+    z: -1
+    cache: true
+    Behavior on opacity { NumberAnimation { duration: Theme.fast; easing.type: Easing.BezierSpline; easing.bezierCurve: Theme.ease } }
+}