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>

src/CMakeLists.txt

@@ -78,12 +78,14 @@ qt_add_executable(sloposk
     backend/InputMethodProtocol.h
     backend/KWinInputMethod.h backend/KWinInputMethod.cpp
     backend/KWinInputContext.h backend/KWinInputContext.cpp
+    backend/KWinFakeInput.h backend/KWinFakeInput.cpp
     backend/WaylandKeymap.h backend/WaylandKeymap.cpp
     window/FloatingWindow.h window/FloatingWindow.cpp
 )
 
 qt6_generate_wayland_protocol_client_sources(sloposk PRIVATE_CODE FILES
     ${WAYLAND_PROTOCOLS_DIR}/unstable/input-method/input-method-unstable-v1.xml
+    ${PROJECT_SOURCE_DIR}/protocols/fake-input.xml
 )
 # Generated code lacks the core-protocol include (see backend/InputMethodProtocol.h).
 set_source_files_properties(${CMAKE_CURRENT_BINARY_DIR}/qwayland-input-method-unstable-v1.cpp