Floating polish: visibility, resize, saved geometry, D-Bus, desktop entry

- VisibilityController: show on field focus, dismiss until next focus,
  manual show/hide/toggle overrides
- FloatingWindow: resize from the corner grip, clamp to screen
- WindowSettings: geometry per screen, debounced saves
- DBusControl: org.sloposk.Keyboard Show/Hide/Toggle for global shortcuts
- org.sloposk.keyboard.desktop so System Settings lists it as a virtual keyboard
- README with build/run/layout docs

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

src/app/DevHooks.cpp

@@ -0,0 +1,38 @@
+#include "DevHooks.h"
+
+#include "backend/TextBackend.h"
+
+#include <QCoreApplication>
+#include <QQuickWindow>
+#include <QTimer>
+
+namespace {
+
+void installAutotype(TextBackend &backend, const QString &text)
+{
+    QObject::connect(&backend, &TextBackend::activeChanged, &backend, [&backend, text] {
+        if (backend.isActive())
+            backend.commitText(text);
+    });
+}
+
+void installScreenshot(QQuickWindow &window, const QString &path)
+{
+    constexpr int SettleMs = 500;
+    QTimer::singleShot(SettleMs, &window, [&window, path] {
+        const bool saved = window.grabWindow().save(path);
+        if (!saved)
+            qWarning("Failed to save screenshot to %s", qPrintable(path));
+        QCoreApplication::exit(saved ? 0 : 1);
+    });
+}
+
+} // namespace
+
+void installDevHooks(TextBackend &backend, QQuickWindow &window)
+{
+    if (const QString text = qEnvironmentVariable("SLOPOSK_AUTOTYPE"); !text.isEmpty())
+        installAutotype(backend, text);
+    if (const QString path = qEnvironmentVariable("SLOPOSK_SCREENSHOT"); !path.isEmpty())
+        installScreenshot(window, path);
+}