Move the synthetic-input toggle to Controllers under Debug details

"Forward synthetic test input" is a controller-debug aid, so it now lives in the
Controllers panel (gated behind Debug details, disabled until the XInput hook is
attached) instead of the Injection panel. ControllersPanel owns the flag and exposes
test_input(); main feeds it into InjectionPanel::set_test_input each frame, so the
existing synthetic-pad substitution in publish() is unchanged.

Verified: x64 build green; review (default view no longer shows it in Injection;
appears in Controllers under Debug details).

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

README.md

@@ -75,12 +75,6 @@ is removed from this list once done — so the top item is always next. The
 self-verifiable tooling / UI / input items come first; the game-pipeline items that
 need a real game (and Remote Play) to fully validate come last.
 
-- **Move the synthetic-input toggle to the Controllers panel, under Debug details.**
-  The "Forward synthetic test input" checkbox is a controller-debugging aid, so move
-  it out of the Injection panel into `ControllersPanel` and gate it behind
-  `debug_details`. The publish path is unchanged (the Injection panel already
-  substitutes the synthetic pattern in `publish`); the flag just moves with it (or is
-  passed from Controllers into the publish call).
 - **Mouse & keyboard forwarding (messages + polling-state hooks).** Forward guest
   clicks and keystrokes into the unfocused game via a new **MKB hook subsystem** in
   `coop_hook.dll` — the toggle *is* the hook (not installed → no forwarding).