Move input polling to its own thread; fixed-width fast-changing UI numbers

Input thread: controller polling, pad publishing, and rumble forwarding were
driven by the render loop, so a low/synced frame rate throttled how often guest
input reached the game. New InputWorker owns the InputSource and runs poll +
IPC publish + rumble on a dedicated ~1 kHz thread, independent of rendering. The
UI thread reads a copy-safe InputSnapshot for the Controllers panel and relays the
Steam-Input request/active/failed state to/from the worker (Steam init/shutdown now
happen on the worker thread). IpcServer gained a mutex so the worker's publish() /
hook_status() can't race the UI thread starting/stopping the shared-memory channel
(use-after-unmap); InjectionPanel::test_input_ is now atomic. ControllersPanel::draw
takes an InputSnapshot instead of the live InputSource.

Fixed-width numbers: fast-changing readouts (menu-bar FPS/ms, Video pipeline rates +
latency + graph legend, controller poll rates + round-trip sticks, audio buffered ms
+ frames/s) printed with %.0f etc., so they shifted/blurred as values crossed digit
thresholds (99 -> 100) each frame. Padded them to fixed field widths so they stay put.

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

host/src/injection_panel.cpp

@@ -256,7 +256,7 @@ void InjectionPanel::reattach()
 
 void InjectionPanel::publish(const std::array<PadInfo, kMaxPads>& pads)
 {
-	if (!test_input_)
+	if (!test_input_.load(std::memory_order_relaxed))
 	{
 		server_.publish(pads);
 		return;