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>

README.md

@@ -114,9 +114,6 @@ From an in-depth review pass. Each item is fixed test-first (a failing test, the
 as its own commit; "verify" items are confirmed real before any change, and dropped if not.
 
 Code quality:
-- **Stale comments** — `hook_guard.hpp` top block (still the old destroy-on-remove model),
-  `input_source.hpp` ("future" Steam source), `audio_ring.hpp` (v1/reserved), `shared_memory.hpp` /
-  `audio_ring.hpp` ("20-byte pads").
 - **Consolidate `VtableHook`** — remove the duplicate copy in `audio_hook.cpp`.
 
 ### Future work