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/ResizeEdge.qml

@@ -0,0 +1,13 @@
+import QtQuick
+
+// Invisible edge/corner grip that hands resizing to the compositor.
+MouseArea {
+    property int edges: 0
+    property var win: Window.window
+    hoverEnabled: true
+    acceptedButtons: Qt.LeftButton
+    cursorShape: edges === (Qt.LeftEdge | Qt.TopEdge) || edges === (Qt.RightEdge | Qt.BottomEdge) ? Qt.SizeFDiagCursor
+               : edges === (Qt.RightEdge | Qt.TopEdge) || edges === (Qt.LeftEdge | Qt.BottomEdge) ? Qt.SizeBDiagCursor
+               : (edges & (Qt.LeftEdge | Qt.RightEdge)) ? Qt.SizeHorCursor : Qt.SizeVerCursor
+    onPressed: win.startSystemResize(edges)
+}