Add focus_spoof_test (and close the dedicated-hook-tests item)

focus_spoof_test plays game + host: it creates a top-level window (which
find_main_window picks up), installs the spoof, and checks that
GetForegroundWindow / GetActiveWindow / GetFocus now report that window, that the
status flag flips on install and off on removal, and that a ClipCursor request is
swallowed while cursor release is the default. Skips if the window can't be
enumerated.

With this and d3d9_hook_test, the dedicated-hook-tests item is done. vk_hook's
present path is intentionally not given a separate in-process test: it's exercised
end to end by mock_game_test's vk-inject path ("hook captured Vulkan present
calls"), and the off-thread VkCapture it drives has vk_capture_perf_test -- a
standalone in-process Vulkan swapchain harness would just duplicate that at high
cost.

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

README.md

@@ -113,9 +113,6 @@ default** and covers anything the hooked path doesn't.
 From an in-depth review pass. Each item is fixed test-first (a failing test, then the fix) and lands
 as its own commit; "verify" items are confirmed real before any change, and dropped if not.
 
-Test coverage:
-- **Dedicated hook tests** — `focus_spoof`, `vk_hook` (present). (`d3d9_hook` done.)
-
 Features:
 - **Static CRT (`/MT`) for `coop_hook.dll`** (x64 + x86) so it loads in games without the VC++ redist.
 - **Stale Vulkan-layer registration cleanup** — remove a leftover `HKCU` implicit-layer entry from a