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>

tests/TestLayouts.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include "layout/KeymapLetters.h"
+#include "layout/LayoutBuilder.h"
+#include "layout/LayoutLoader.h"
+
+#include <QTest>
+#include <xkbcommon/xkbcommon.h>
+
+#include <memory>
+
+// Builds layouts the way the app does: the built-in template filled from a
+// keymap, here compiled from XKB names instead of received from a compositor.
+// Q_INIT_RESOURCE can't be used inside a namespace.
+inline void initLayoutResources() { Q_INIT_RESOURCE(layouts); }
+
+namespace TestLayouts {
+
+inline Layout builtinTemplate()
+{
+    initLayoutResources();
+    QString error;
+    const auto layout = LayoutLoader::load(QStringLiteral(":/layouts/template.json"), &error);
+    if (!layout)
+        qFatal("template.json: %s", qPrintable(error));
+    return *layout;
+}
+
+inline KeymapLetters letters(const char *layout, const char *variant = nullptr)
+{
+    const std::unique_ptr<xkb_context, void (*)(xkb_context *)> context(
+        xkb_context_new(XKB_CONTEXT_NO_ENVIRONMENT_NAMES), xkb_context_unref);
+    const xkb_rule_names names{.rules = "evdev", .model = "pc105", .layout = layout, .variant = variant,
+                               .options = nullptr};
+    const std::unique_ptr<xkb_keymap, void (*)(xkb_keymap *)> keymap(
+        xkb_keymap_new_from_names(context.get(), &names, XKB_KEYMAP_COMPILE_NO_FLAGS), xkb_keymap_unref);
+    if (!keymap)
+        qFatal("no XKB keymap for %s", layout);
+    return readKeymapLetters(keymap.get(), 0);
+}
+
+inline Layout build(const char *layout, const char *variant = nullptr)
+{
+    return buildLayout(builtinTemplate(), letters(layout, variant));
+}
+
+} // namespace TestLayouts