Phase 1a: per-slot poll viz + input-path diagnostics

Surfaced by a game (Life is Strange: Before the Storm) that ignores
controller input when it lacks true OS focus even though it still polls
XInput. To find the focus-gated detection path, instrument the hook.

Protocol v3 status back-channel now reports:
- per-slot XInputGetState and XInputGetCapabilities counters (replacing the
  single aggregate), so the overlay shows exactly which slots the game polls
  and how fast;
- focus-API call counts (GetForegroundWindow/GetActiveWindow/GetFocus) to see
  whether the game consults the APIs we spoof;
- input-path diagnostics: whether the process registered Raw Input for a
  gamepad usage and whether it set RIDEV_INPUTSINK (background delivery), and
  whether a DirectInput dll is loaded.

Host overlay gains a per-slot poll table and an "Input path" section. The DLL
refreshes input diagnostics each worker tick via GetRegisteredRawInputDevices.
hook_selftest updated for per-slot counters; passes.

This is diagnostic-only: once a real run shows which path LiS uses, the
targeted focus fix (e.g. forcing RIDEV_INPUTSINK or DI background coop) follows.

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

hook/src/focus_spoof.hpp

@@ -15,6 +15,11 @@ namespace coop::hook
 // status through `ipc`.
 bool install_focus_spoof(IpcClient& ipc);
 
+// Reports how the game currently reads input (Raw Input gamepad usage + sink
+// flag, DirectInput presence) so the host can identify a focus-gated path. Cheap
+// to call each tick.
+void update_input_diagnostics(IpcClient& ipc);
+
 // Restores the original window procedure and removes the focus API hooks.
 void remove_focus_spoof();