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/Main.qml

@@ -6,7 +6,9 @@ Window {
 
     required property LayoutModel layoutModel
     required property KeyboardController controller
+    required property Settings settings
     property var placement: null // FloatingWindow, set from C++
+    property bool settingsOpen: false
 
     // Transparent room above the keyboard for long-press popups on the top row.
     readonly property real popupMargin: 90
@@ -35,16 +37,29 @@ Window {
             id: keyboard
             anchors { left: parent.left; right: parent.right; top: parent.top; bottom: handle.top }
             anchors.margins: 2
+            visible: !root.settingsOpen
             model: root.layoutModel
             controller: root.controller
         }
 
+        SettingsPanel {
+            anchors.fill: keyboard
+            visible: root.settingsOpen
+            settings: root.settings
+        }
+
         DragHandle {
             id: handle
             anchors { left: parent.left; right: parent.right; bottom: parent.bottom }
             onMoved: (dx, dy) => root.placement?.moveBy(dx, dy)
         }
 
+        SettingsButton {
+            anchors { left: parent.left; leftMargin: 8; bottom: parent.bottom }
+            checked: root.settingsOpen
+            onClicked: root.settingsOpen = !root.settingsOpen
+        }
+
         ResizeHandle {
             anchors { right: parent.right; bottom: parent.bottom }
             onResized: (dw, dh) => root.placement?.resizeBy(dw, dh)