Phase 1a: input forwarding via DLL injection + XInput hook

The host can now inject coop_hook.dll into a running game and forward
controller state to it over shared memory, so the game reads the host's
(eventually the guest's) input and nothing else.

- hook/: coop_hook.dll. DllMain spawns a worker that opens the shared-memory
  channel (named by the game's pid) and installs SafetyHook inline hooks on
  XInputGetState/GetStateEx/GetCapabilities/SetState. Detours synthesize state
  from shared memory; unmanaged slots report disconnected, hiding physical pads.
- host/: process picker (Toolhelp32), CreateRemoteThread(LoadLibraryW) injector
  with an IsWow64Process2 bitness guard, IPC server publishing pads each frame,
  and an ImGui Injection panel wiring it together.
- tests/: hook_selftest exercises the IPC seqlock + hook detours in-process
  (no game/controller needed); passes.

Build: SafetyHook wired in (COOP_BUILD_HOOK=ON), Zydis via FetchContent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

host/src/main.cpp

@@ -14,6 +14,7 @@
 #include "d3d11_window.hpp"
 #include "debug_overlay.hpp"
 #include "imgui_layer.hpp"
+#include "injection_panel.hpp"
 #include "input/xinput_source.hpp"
 
 namespace
@@ -36,13 +37,16 @@ int run()
 	}
 
 	auto input = std::make_unique<coop::XInputSource>();
+	coop::InjectionPanel injection;
 
 	while (window.pump_messages())
 	{
 		input->poll();
+		injection.publish(input->pads());
 
 		imgui.begin_frame();
 		coop::draw_debug_overlay(*input);
+		injection.draw();
 
 		window.render_frame([&imgui]() { imgui.end_frame(); });
 	}