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/MessageBar.qml

@@ -0,0 +1,30 @@
+import QtQuick
+
+// Excel's yellow message bar, for notices.
+Rectangle {
+    id: mb
+    property string text: ""
+    height: text ? 32 : 0
+    visible: text !== ""
+    color: "#FFF4CE"
+    Rectangle { anchors.bottom: parent.bottom; width: parent.width; height: 1; color: "#E6D9A8" }
+    Behavior on height { NumberAnimation { duration: X.easeMs } }
+    function show(t) { text = t; hide.restart() }
+    Timer { id: hide; interval: 6000; onTriggered: mb.text = "" }
+    Row {
+        x: 12
+        height: parent.height
+        spacing: 10
+        Ico { anchors.verticalCenter: parent.verticalCenter; name: "info"; size: 16 }
+        T { height: parent.height; text: "NOTICE"; font.bold: true }
+        T { height: parent.height; text: mb.text }
+    }
+    Item {
+        anchors { right: parent.right; rightMargin: 8; verticalCenter: parent.verticalCenter }
+        width: 22
+        height: 22
+        Rectangle { anchors.fill: parent; color: xm.containsMouse ? "#F2E2A6" : "transparent" }
+        Ico { anchors.centerIn: parent; name: "close"; size: 18 }
+        MouseArea { id: xm; anchors.fill: parent; hoverEnabled: true; onClicked: mb.text = "" }
+    }
+}