refactor(gamepad/windows): drop the dead shell fork, use pf-client-core's service

clients/windows/src/gamepad.rs was a 629-line near-verbatim fork of
pf-client-core's SDL gamepad service, frozen at an old single-pad design.
Commit 9822fc3b removed its attach/detach entry points but left the machinery,
so `Worker.attached` was initialized None and never set — ~300-400 lines
(button/axis/touchpad/motion forwarding, Ds5Feedback, the rumble/HID feedback
loop) were logically unreachable, never flagged because the guards read a
runtime Option the compiler can't prove is always None. The live remainder
(pad enumeration + pin persistence) had drifted from core: it opened every
device for metadata (vs core's no-open id-getters), force-enabled the Valve
HIDAPI drivers unconditionally, lacked the steam_virtual skip (so it could pin
Steam Input's virtual pad and kill gyro), and derived the pin key from an
opened handle — risking a cross-process byte-mismatch with the session, which
resolves the same key from id-getters.

The shell's only live job is enumerating pads for the Settings list and
persisting the pin; the spawned punktfunk-session already runs the full
pf-client-core service and does all real forwarding (session/main.rs). So
delete the fork and point the shell at pf_client_core::gamepad::GamepadService
directly — its start()/pads()/set_pinned()/clone() + PadInfo{key,name,
kind_label()} are a strict superset of what the shell uses. Idle, core's
service is hands-off the hardware (id-getter metadata, no device open, HIDAPI
off), which is the intended behavior and fixes the drift class above.

- delete clients/windows/src/gamepad.rs (-629) and `mod gamepad;`
- main.rs / app/mod.rs: use pf_client_core::gamepad::GamepadService
- drop the now-unused direct sdl3 dep (pf-client-core pulls it on Windows with
  the same build-from-source,hidapi features); sync Cargo.lock

Pre-checks (dev Mac): std mpsc Sender<T>: Sync confirmed on the pinned 1.96.0
(so core's GamepadService is Sync for the WinUI cross-thread sharing, no core
change needed); rustfmt clean; no dangling refs. Windows compile is deferred
to CI (windows-only crate, unbuildable on macOS).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/windows/src/main.rs

@@ -24,8 +24,6 @@ mod app;
 #[cfg(windows)]
 mod discovery;
 #[cfg(windows)]
-mod gamepad;
-#[cfg(windows)]
 mod gpu;
 #[cfg(windows)]
 mod probe;
@@ -85,7 +83,11 @@ fn main() {
         tracing::error!(error = %e, "Windows App SDK bootstrap failed");
         std::process::exit(1);
     }
-    let gamepad = gamepad::GamepadService::start();
+    // The shared SDL gamepad service (pf-client-core). The shell only enumerates pads (Settings
+    // list) and persists the pin; the spawned punktfunk-session runs the SAME service and does the
+    // actual forwarding — so, unlike the old shell fork, we never `attach()` here. Idle it stays
+    // hands-off the hardware (id-getter metadata, no device open, Valve HIDAPI drivers off).
+    let gamepad = pf_client_core::gamepad::GamepadService::start();
     if let Err(e) = app::run(identity, gamepad) {
         tracing::error!(error = %e, "WinUI app failed");
         std::process::exit(1);