Consolidate the duplicated VtableHook into one shared copy

audio_hook.cpp carried its own VtableHook class identical to the shared
hook/src/vtable_hook.hpp -- two copies of the same delicate vtable-swap unhook
logic to keep in sync. Drop the audio copy and use the shared one (it's in
namespace coop::hook, so the in-file references resolve to it), leaving a short
note on why WASAPI methods are vtable-swapped rather than inline-hooked. Update
the shared header's comment to name both users (audio + DirectInput).

Last item from the review pass -- the Roadmap's Current-work section is now empty
(done work lives in git history); only Future work remains. Validated by
audio_hook_test (the vtable swap still hooks GetService/GetBuffer/ReleaseBuffer
end to end).

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

README.md

@@ -108,14 +108,6 @@ default** and covers anything the hooked path doesn't.
 
 ## Roadmap
 
-### Current work
-
-From an in-depth review pass. Each item is fixed test-first (a failing test, then the fix) and lands
-as its own commit; "verify" items are confirmed real before any change, and dropped if not.
-
-Code quality:
-- **Consolidate `VtableHook`** — remove the duplicate copy in `audio_hook.cpp`.
-
 ### Future work
 
 - **Per-game profiles** — persist each game's subsystem / capture-mode / audio choices and re-apply