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/StatusChip.qml

@@ -0,0 +1,28 @@
+import QtQuick
+
+Rectangle {
+    id: chip
+    property string status: "queued"
+    property real progress: 0
+    readonly property color tone: status === "done" ? Theme.success
+                                : status === "error" ? Theme.error
+                                : status === "running" ? Theme.primary : Theme.textLo
+    readonly property string label: status === "running" ? Math.floor(progress * 100) + "%"
+                                  : status === "done" ? "Done"
+                                  : status === "error" ? "Failed"
+                                  : status === "cancelled" ? "Cancelled" : "Queued"
+    implicitWidth: t.implicitWidth + 16
+    implicitHeight: 20
+    radius: 10
+    color: Theme.alpha(tone, 0.16)
+    border.color: Theme.alpha(tone, 0.35)
+    Txt {
+        id: t
+        anchors.centerIn: parent
+        text: chip.label
+        color: chip.tone
+        font.pixelSize: 11
+        font.weight: Font.DemiBold
+        font.features: { "tnum": 1 }
+    }
+}