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>

hook/src/xinput_hook.cpp

@@ -19,7 +19,7 @@ namespace
 // XInputGetStateEx that many games use. Mirrors how Steam/x360ce expose it.
 constexpr std::uint16_t kGuideButton = 0x0400;
 
-const IpcClient* g_ipc = nullptr;
+IpcClient* g_ipc = nullptr;
 std::vector<safetyhook::InlineHook> g_hooks;
 
 // Last good snapshot, so a momentary failed IPC read (host mid-write) doesn't
@@ -62,6 +62,10 @@ DWORD query_state(DWORD user_index, XINPUT_STATE* state, bool keep_guide)
 	{
 		return ERROR_DEVICE_NOT_CONNECTED;
 	}
+	if (g_ipc != nullptr)
+	{
+		g_ipc->note_query(user_index); // proves to the host the game is polling us
+	}
 	refresh_cache();
 	const CoopPadState& pad = g_cache[user_index];
 	if (!pad.connected)
@@ -156,7 +160,7 @@ void hook_ordinal(HMODULE module, WORD ordinal, void* detour)
 
 } // namespace
 
-bool install_xinput_hooks(const IpcClient& ipc)
+bool install_xinput_hooks(IpcClient& ipc)
 {
 	if (!g_hooks.empty())
 	{
@@ -180,7 +184,12 @@ bool install_xinput_hooks(const IpcClient& ipc)
 		hook_export(module, "XInputGetCapabilities", reinterpret_cast<void*>(&hk_XInputGetCapabilities));
 		hook_export(module, "XInputSetState", reinterpret_cast<void*>(&hk_XInputSetState));
 	}
-	return !g_hooks.empty();
+	if (!g_hooks.empty())
+	{
+		g_ipc->mark_attached();
+		return true;
+	}
+	return false;
 }
 
 void remove_xinput_hooks()