add slide-in applet dock with collapsible cards, edge trigger, and bar module toggle

shell/dock/DockState.qml

@@ -0,0 +1,29 @@
+pragma Singleton
+
+import QtQuick
+
+QtObject {
+    // "closed" | "pinned" | "overlay"
+    property string mode: "closed"
+    readonly property bool open: mode !== "closed"
+
+    function openPinned() {
+        mode = "pinned";
+    }
+
+    function openOverlay() {
+        if (mode === "closed")
+            mode = "overlay";
+    }
+
+    function close() {
+        mode = "closed";
+    }
+
+    function toggle() {
+        if (mode === "pinned")
+            mode = "closed";
+        else
+            mode = "pinned";
+    }
+}