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.
andrew
61c448eb00