Fix double-space period, shift double-tap; settings; letters from system keymap

- Double-space replaced the space via a Backspace keysym, which clients
  apply after the commit: use delete_surrounding_text with the commit
- Tests use a shared FakeEngine that applies ops to a simulated field
- Double-tap shift locks at a sentence start; typing between taps doesn't
- Organization name set: config lives in ~/.config/sloposk/
- Settings (auto-capitalization, double-space period) with a ⚙ panel
- Letter rows come from the compositor's XKB keymap; other letters of the
  layout become long-press alternates; globe switches the system layout
  over org.kde.keyboard
- One JSON template for non-letter layers; stretch keys even out rows

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

qml/ToggleRow.qml

@@ -0,0 +1,57 @@
+import QtQuick
+
+// A labelled on/off switch in the iOS style.
+Item {
+    id: row
+
+    required property string text
+    property string detail: ""
+    property bool checked: false
+    signal toggled(bool checked)
+
+    implicitHeight: 52
+
+    Column {
+        anchors { left: parent.left; right: track.left; rightMargin: 12; verticalCenter: parent.verticalCenter }
+        spacing: 2
+
+        Text {
+            width: parent.width
+            text: row.text
+            color: Theme.text
+            font.pixelSize: 16
+            elide: Text.ElideRight
+        }
+        Text {
+            width: parent.width
+            visible: text !== ""
+            text: row.detail
+            color: Theme.secondaryText
+            font.pixelSize: 12
+            elide: Text.ElideRight
+        }
+    }
+
+    Rectangle {
+        id: track
+        anchors { right: parent.right; verticalCenter: parent.verticalCenter }
+        width: 50
+        height: 30
+        radius: height / 2
+        color: row.checked ? Theme.toggleOn : Theme.functionKey
+
+        Rectangle {
+            x: row.checked ? parent.width - width - 2 : 2
+            anchors.verticalCenter: parent.verticalCenter
+            width: parent.height - 4
+            height: width
+            radius: width / 2
+            color: "#ffffff"
+            Behavior on x { NumberAnimation { duration: 120 } }
+        }
+    }
+
+    TapHandler {
+        onTapped: row.toggled(!row.checked)
+    }
+}