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>

hook/CMakeLists.txt

@@ -0,0 +1,15 @@
+add_library(coop_hook SHARED
+	src/dllmain.cpp
+	src/xinput_hook.cpp)
+
+target_include_directories(coop_hook PRIVATE src)
+
+target_link_libraries(coop_hook PRIVATE
+	coop_common
+	safetyhook::safetyhook)
+
+set_target_properties(coop_hook PROPERTIES OUTPUT_NAME "coop_hook")
+
+# TODO(dist): statically link the VC runtime (/MT) so the DLL loads in games on
+# machines without the matching VC redist. Deferred until SafetyHook + Zydis are
+# also forced to a static CRT to avoid a /MT-vs-/MD mismatch.