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/Cargo.toml

@@ -62,10 +62,10 @@ windows = { git = "https://github.com/microsoft/windows-rs", rev = "a4f7b2cb7c63
 # decode + present live in the spawned punktfunk-session binary.)
 ffmpeg-next = "8"
 
-# Gamepads: capture + feedback (full DualSense fidelity needs hidapi). SDL3 is cross-platform;
-# built from source via the bundled CMake on Windows (no system SDL3).
-sdl3 = { version = "0.18", features = ["build-from-source", "hidapi"] }
-
+# Gamepad enumeration + pin persistence for Settings runs on pf-client-core's shared SDL service
+# (see the `gamepad` field in app/); the spawned punktfunk-session does the actual forwarding. SDL3
+# itself (built from source via the bundled CMake on Windows) is pulled transitively by
+# pf-client-core with the same `build-from-source,hidapi` features, so it is not a direct dep here.
 mdns-sd = "0.20"
 async-channel = "2"
 serde = { version = "1", features = ["derive"] }