Full keyboard mode, Ctrl/Alt/Super, dead keys, shift levels

- Full (iPad Pro) mode: every typing key from the keymap, number row,
  tab, caps lock, ctrl/super/alt; shifted symbol shown above and flickable
- Dead keys compose with the locale's XKB compose table
- Ctrl/Alt/Super stick like shift and turn keys into shortcuts; a tapped
  or held shift joins shortcuts and non-text keys, auto-shift and caps
  lock don't
- Auto-capitalization and caps lock only capitalize letters; the user's
  shift picks the keymap's shifted level
- Mode switch in settings keeps key size by resizing the window

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

qml/SettingsPanel.qml

@@ -47,6 +47,14 @@ Rectangle {
 
             SectionHeader { text: qsTr("Keys") }
 
+            ToggleRow {
+                width: parent.width
+                text: qsTr("Full Keyboard")
+                detail: qsTr("Number row, tab, ctrl, alt — like iPad Pro")
+                checked: panel.settings.fullKeyboard
+                onToggled: checked => panel.settings.fullKeyboard = checked
+            }
+
             Repeater {
                 // "main" is the typing keys; the rest come from the template.
                 model: [{ id: "main", name: qsTr("Typing keys") }].concat(panel.layoutModel.sections)