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/CMakeLists.txt

@@ -3,7 +3,11 @@ add_executable(coop_host WIN32
 	src/d3d11_window.cpp
 	src/imgui_layer.cpp
 	src/debug_overlay.cpp
-	src/input/xinput_source.cpp)
+	src/injection_panel.cpp
+	src/input/xinput_source.cpp
+	src/inject/process_list.cpp
+	src/inject/injector.cpp
+	src/ipc/ipc_server.cpp)
 
 target_include_directories(coop_host PRIVATE src)