Fix stale removal comments (persistent, not destroy) + add deterministic install test

- The remove_* comments still described the superseded "disable -> drain -> destroy"
  flow; the code keeps hooks alive (persistent) and re-enables on re-install. Updated
  the comments to match, and corrected the XInput note (its detours return synthesized
  state and never call the trampoline, so destroying its vector is safe -- unlike the
  trampoline-calling present/MKB/focus-cursor hooks).
- hook_install_test: a fast, single-threaded contract test for hook_install.hpp --
  install_inline creates the hook once and reuses the SAME trampoline across 50
  install/remove cycles (never freed -> no stale-detour UAF), toggling enable/disable
  cleanly. Fills the guard the removed (flaky, concurrency-bound) reproducer left, with
  no threads so it can't flake on SafetyHook's enable/disable atomicity.

x64 23/23, x86 3/3.

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

hook/src/focus_spoof.cpp

@@ -314,7 +314,6 @@ void remove_focus_spoof()
 	// patched bytes. The reverse of the enable order (GFW first) keeps the invariant "GetActiveWindow
 	// hooked => GetForegroundWindow hooked" across the whole install/remove cycle, so a call never
 	// lands in a half-patched shared region (the intermittent storm crash: GetActiveWindow+0x8).
-	// Disable (not destroy) keeps the trampolines alive for any in-flight detour; destroy after drain.
 	for (auto it = g_focus_hooks.rbegin(); it != g_focus_hooks.rend(); ++it)
 	{
 		disable_for_removal(*it);