Fix stale comments

- hook_guard.hpp top block: described removal as `hook = {}` (destroy/reset); the
  model is now persistent disable_for_removal (never destroyed mid-session, the
  trampoline stays alive). Updated to match.
- input_source.hpp: SteamInputSource is no longer "future" -- it exists and is
  opt-in; reworded.
- audio_ring.hpp: format_generation actually bumps on every set_format (not
  "reserved, v1 sets once"); verify_capture is a 4-byte atomic guarded by the
  version gate (not "repurposed from a reserved byte old builds saw"); and the
  SharedBlock is no longer "20-byte pads".
- audio_format_verifier.cpp: dropped a dead `(void)recover_layout;` with a stale
  "step (a) only" comment -- the parameter is actually used.

Comment-only except the dead (void) cast.

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

host/src/audio/audio_format_verifier.cpp

@@ -132,7 +132,6 @@ ChunkedCapture parse_chunks(const std::vector<BYTE>& raw, unsigned stride)
 
 FormatVerification verify_stream_format(DWORD pid, AudioRingHeader* ring, unsigned window_ms, bool recover_layout)
 {
-	(void)recover_layout; // step (b) extends this; step (a) recovers the rate only
 	FormatVerification result;
 	if (ring == nullptr)
 	{

host/src/input/input_source.hpp

@@ -1,9 +1,10 @@
 // Abstraction over "where controller input comes from" on the host side.
 //
-// Phase 0/1 use XInputSource: Remote Play Together delivers each guest's gamepad
-// to the focused window (our host) as a virtual XInput controller, so reading
-// XInput is enough to see guests. A future SteamInputSource can implement this
-// same interface for cleaner per-guest handles once the Steamworks SDK is wired.
+// XInputSource is the primary/default: Remote Play Together delivers each guest's gamepad to the
+// focused window (our host) as a virtual XInput controller, so reading XInput is enough to see guests.
+// SteamInputSource (steam_input_source.cpp) implements this same interface over Steam Input when the
+// Steamworks SDK is present; it's opt-in (initializing Steam Input suppresses XInput -- see the
+// Controllers panel and Lessons learned).
 #pragma once
 
 #include <array>