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>

tests/hook_selftest.cpp

@@ -77,6 +77,10 @@ int main()
 	check(XInputGetCapabilities(0, 0, &caps) == ERROR_SUCCESS, "slot 0 capabilities reported");
 	check(caps.Type == XINPUT_DEVTYPE_GAMEPAD, "capability device type");
 
+	// Status back-channel: the host relies on these to prove the hook is live.
+	check(block->status.attached == 1, "status reports attached");
+	check(block->status.xinput_queries.load(std::memory_order_relaxed) >= 2, "status counts XInput queries");
+
 	hook::remove_xinput_hooks();
 
 	std::printf(g_failures == 0 ? "SELFTEST PASS\n" : "SELFTEST FAILED (%d)\n", g_failures);