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/Ico.qml

@@ -0,0 +1,15 @@
+import QtQuick
+
+// image://icon/<name>[/<hex ink>], rendered at device pixels.
+Image {
+    property string name: "grid"
+    property string ink: ""
+    property int size: 16
+    width: size
+    height: size
+    source: "image://icon/" + name + (ink ? "/" + ink.replace("#", "") : "")
+    sourceSize.width: size * Screen.devicePixelRatio
+    sourceSize.height: size * Screen.devicePixelRatio
+    smooth: true
+    asynchronous: false
+}