Phase 1a: focus spoofing + hook observability

Two problems surfaced in testing: (1) no way to tell whether the injected
hook was actually the input source, and (2) the final design needs the tool
window focused for Steam RPT capture, which would pause/silence games that
react to focus loss. Both are addressed here.

- Focus spoofing (hook/focus_spoof): find the game's main window, subclass it
  to rewrite/swallow WM_ACTIVATE/ACTIVATEAPP/NCACTIVATE/KILLFOCUS, and inline-
  hook GetForegroundWindow/GetActiveWindow/GetFocus to always report the game
  as active. The game keeps running and polling while unfocused.
- Status back-channel (protocol v2): the DLL reports attached/focus-spoof
  flags, game pid/hwnd, a heartbeat, and a cumulative XInputGetState counter.
  The host overlay turns the counter into a live poll rate, so "is the hook
  working" is directly observable.
- Synthetic test-input toggle in the host: forwards a known automated pattern
  (stick circle + periodic A) to prove forwarding independent of the physical
  pad.
- hook_selftest extended to assert the status channel; passes.

Documented the windowed/borderless requirement and the new observable test
flow in the README.

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

host/src/ipc/ipc_server.hpp

@@ -3,6 +3,7 @@
 #pragma once
 
 #include <array>
+#include <cstdint>
 
 #include "coop/protocol.hpp"
 #include "coop/shared_memory.hpp"
@@ -11,6 +12,18 @@
 namespace coop
 {
 
+// Plain (non-atomic) snapshot of the hook's back-channel for the overlay.
+struct HookStatusView
+{
+	bool attached = false;       // XInput hooks installed in the game
+	bool focus_spoof = false;    // focus spoofing active
+	std::uint32_t heartbeat = 0; // DLL liveness counter
+	std::uint64_t xinput_queries = 0;
+	std::uint32_t game_pid = 0;
+	std::uint64_t game_hwnd = 0;
+	std::uint32_t last_user_index = 0;
+};
+
 class IpcServer
 {
 public:
@@ -23,6 +36,9 @@ public:
 
 	void stop();
 
+	// Reads the hook's diagnostics back-channel (zeroed if not started).
+	[[nodiscard]] HookStatusView hook_status() const;
+
 	[[nodiscard]] bool running() const
 	{
 		return block_ != nullptr;