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/SheetTabs.qml

@@ -0,0 +1,89 @@
+import QtQuick
+
+// Worksheet tabs. The first six are fixed; opened artists, albums, playlists and searches follow.
+Rectangle {
+    id: st
+    property var win: Window.window
+    height: 26
+    color: X.ribbon
+    Rectangle { width: parent.width; height: 1; color: X.ribbonLine }
+
+    Row {
+        id: nav
+        x: 6
+        height: parent.height
+        spacing: 2
+        Repeater {
+            model: ["left", "right"]
+            delegate: Item {
+                required property int index
+                required property string modelData
+                width: 18
+                height: parent.height
+                Ico { anchors.centerIn: parent; name: parent.modelData; size: 12; opacity: na.containsMouse ? 1 : 0.6 }
+                MouseArea {
+                    id: na
+                    anchors.fill: parent
+                    hoverEnabled: true
+                    onClicked: library.current = Math.max(0, Math.min(library.tabs.length - 1, library.current + (parent.index ? 1 : -1)))
+                }
+            }
+        }
+    }
+
+    Flickable {
+        id: flick
+        x: nav.x + nav.width + 8
+        width: parent.width - x - 8
+        height: parent.height
+        contentWidth: tabRow.width + 40
+        clip: true
+        flickableDirection: Flickable.HorizontalFlick
+        boundsBehavior: Flickable.StopAtBounds
+        Row {
+            id: tabRow
+            height: parent.height
+            Repeater {
+                model: library.tabs
+                delegate: Item {
+                    id: tb
+                    required property int index
+                    required property var modelData
+                    readonly property bool active: library.current === index
+                    width: lbl.implicitWidth + 28
+                    height: st.height
+                    Rectangle {
+                        anchors.fill: parent
+                        anchors.topMargin: 0
+                        color: tb.active ? "#FFFFFF" : tm.containsMouse ? "#E5E5E5" : "transparent"
+                    }
+                    Rectangle { visible: !tb.active; anchors.right: parent.right; y: 6; width: 1; height: parent.height - 12; color: "#C8C8C8" }
+                    Rectangle { visible: tb.active; anchors.bottom: parent.bottom; width: parent.width; height: 3; color: X.green }
+                    T {
+                        id: lbl
+                        anchors.centerIn: parent
+                        text: tb.modelData.title
+                        color: tb.active ? X.greenText : X.ink
+                        font.bold: tb.active
+                    }
+                    MouseArea {
+                        id: tm
+                        anchors.fill: parent
+                        hoverEnabled: true
+                        acceptedButtons: Qt.LeftButton | Qt.MiddleButton
+                        onClicked: (m) => m.button === Qt.MiddleButton ? library.closeTab(tb.index) : (library.current = tb.index)
+                    }
+                    Tip { target: tm; text: tb.modelData.base ? "" : "Middle-click or Backspace to close" }
+                }
+            }
+            // ⊕ new sheet: here, the search box
+            Item {
+                width: 30
+                height: st.height
+                Ico { anchors.centerIn: parent; name: "plus"; size: 16; opacity: pm.containsMouse ? 1 : 0.6 }
+                MouseArea { id: pm; anchors.fill: parent; hoverEnabled: true; onClicked: st.win.focusSearch() }
+                Tip { target: pm; text: "New sheet from a search" }
+            }
+        }
+    }
+}