Add SDL3-based controller input service

Integrate SDL3 controller support and wire it into the InputRouter.

- Add ControllerInputService (src/ControllerInputService.{h,cpp}) to discover, poll and translate SDL3 gamepad events into InputRouter actions, with axis repeat handling and debouncing.
- Update CMakeLists to find or fetch SDL3, add the new source files to the target, link the SDL3 target, and copy runtime DLLs on Windows.
- Add triggerAction(Action) to InputRouter and use it from existing keyboard handling to centralize action dispatch.
- Instantiate ControllerInputService in main so controllers feed the InputRouter.
- Update QML views (ShellWindow, HomeView, LibraryView, SettingsView) to use numeric action IDs and add small UI/status text and navigation tweaks for controller-driven flows.

These changes enable gamepad/controller input for Bigscreen via SDL3 and adapt UI code to handle the mapped actions.

Bigscreen/CMakeLists.txt

@@ -9,6 +9,30 @@ set(CMAKE_AUTOMOC ON)
 set(CMAKE_AUTORCC ON)
 
 find_package(Qt6 6.5 REQUIRED COMPONENTS Quick Gui)
+find_package(SDL3 CONFIG QUIET)
+
+if(NOT SDL3_FOUND)
+    include(FetchContent)
+    set(SDL_SHARED ON CACHE BOOL "" FORCE)
+    set(SDL_STATIC OFF CACHE BOOL "" FORCE)
+    set(SDL_TEST_LIBRARY OFF CACHE BOOL "" FORCE)
+    set(SDL_TESTS OFF CACHE BOOL "" FORCE)
+    set(SDL_EXAMPLES OFF CACHE BOOL "" FORCE)
+
+    FetchContent_Declare(SDL3
+        URL https://github.com/libsdl-org/SDL/releases/download/release-3.2.30/SDL3-3.2.30.tar.gz
+        DOWNLOAD_EXTRACT_TIMESTAMP TRUE
+    )
+    FetchContent_MakeAvailable(SDL3)
+endif()
+
+if(TARGET SDL3::SDL3)
+    set(BIGSCREEN_SDL_TARGET SDL3::SDL3)
+elseif(TARGET SDL3::SDL3-shared)
+    set(BIGSCREEN_SDL_TARGET SDL3::SDL3-shared)
+else()
+    message(FATAL_ERROR "SDL3 target was not found after package lookup/fetch")
+endif()
 
 qt_standard_project_setup(REQUIRES 6.5)
 qt_policy(SET QTP0004 NEW)
@@ -31,6 +55,8 @@ set_source_files_properties(qml/Theme.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
 
 qt_add_executable(nebula-bigscreen
     src/main.cpp
+    src/ControllerInputService.cpp
+    src/ControllerInputService.h
     src/InputRouter.cpp
     src/InputRouter.h
 )
@@ -45,8 +71,21 @@ target_link_libraries(nebula-bigscreen
     PRIVATE
         Qt6::Quick
         Qt6::Gui
+        ${BIGSCREEN_SDL_TARGET}
 )
 
+if(WIN32)
+    add_custom_command(
+        TARGET nebula-bigscreen
+        POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different
+            $<TARGET_RUNTIME_DLLS:nebula-bigscreen>
+            $<TARGET_FILE_DIR:nebula-bigscreen>
+        COMMAND_EXPAND_LISTS
+        COMMENT "Copying runtime DLLs next to nebula-bigscreen"
+    )
+endif()
+
 if(WIN32)
     set_target_properties(nebula-bigscreen PROPERTIES WIN32_EXECUTABLE TRUE)