Type into any window: fake input when no text field is focused

- KWinFakeInput (org_kde_kwin_fake_input v6, offered by KWin to the
  input-method process): keysyms with real modifier keys held
- The KWin backend uses the input method in text fields and fake input
  everywhere else, so shortcuts, terminals and the desktop get keys
- Text rules (auto-capitalization, double-space) only apply in fields
- Always Show setting keeps the keyboard up without a text field

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

data/org.sloposk.keyboard.desktop

@@ -6,3 +6,5 @@ Type=Application
 Icon=input-keyboard-virtual
 NoDisplay=true
 X-KDE-Wayland-VirtualKeyboard=true
+# Key events for windows without a text field (fake input is restricted).
+X-KDE-Wayland-Interfaces=org_kde_kwin_fake_input