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/Tip.qml

@@ -0,0 +1,18 @@
+import QtQuick
+import QtQuick.Controls.Basic
+
+ToolTip {
+    id: tip
+    delay: 600
+    timeout: 4000
+    padding: 8
+    contentItem: Txt { text: tip.text; font.pixelSize: Theme.fs12 }
+    background: Rectangle {
+        color: Theme.surface2
+        radius: 6
+        border.color: Theme.outline
+        Elevation { level: 2; radius: 6 }
+    }
+    enter: Transition { NumberAnimation { property: "opacity"; from: 0; to: 1; duration: Theme.fast } }
+    exit: Transition { NumberAnimation { property: "opacity"; from: 1; to: 0; duration: Theme.fast } }
+}