fix(inject/host/windows): fold Steam back grips on the Windows DS/DS4 backends (G7)

The Windows DualSense and DualShock 4 managers passed the raw wire
buttons straight into `DsState::from_gamepad`, so a client's Steam back
grips (BTN_PADDLE1..4) were silently dropped and `PUNKTFUNK_STEAM_REMAP`
was ignored — the Linux DS/DS4 backends already fold them via
`steam_remap::fold_paddles`. Bring the Windows backends to parity: add a
`remap: steam_remap::RemapConfig` field (`::from_env()` in `new()`) to
both managers and fold the paddles before `from_gamepad`, exactly as
`linux/dualsense.rs` / `linux/dualshock4.rs`. Default policy stays Drop
(don't fire buttons the user didn't ask for); set the env to map the
grips onto stick-clicks or shoulders.

`steam_remap` was gated `target_os = "linux"`; widened to
`any(linux, windows)`. It's pure (only punktfunk_core + std::env); its
Linux-only Deck motion rescale is `pub` so it compiles clean on Windows
with no dead-code warning.

Verified: Linux .21 (clippy -D warnings clean, inject tests 32 pass / 0
fail — the gate widening is a no-op there); Windows .173 (clean-recheck
of punktfunk-host, cargo clippy --all-targets -D warnings EXITCODE 0,
steam_remap + both managers compiling on Windows for the first time).
On-glass with a real DualSense/DS4 + PUNKTFUNK_STEAM_REMAP still owed.

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

crates/punktfunk-host/src/inject.rs

@@ -527,7 +527,9 @@ pub mod steam_gadget;
 #[path = "inject/proto/steam_proto.rs"]
 pub mod steam_proto;
 /// Pure fallback-remap policy (Steam-only inputs onto a non-Steam backend) + the Deck motion rescale.
-#[cfg(target_os = "linux")]
+/// Shared by the Linux and Windows DualSense/DS4 backends (the slot-less pads that must fold the
+/// Steam back grips); the Deck motion rescale is Linux-only but harmless to compile on Windows.
+#[cfg(any(target_os = "linux", target_os = "windows"))]
 #[path = "inject/proto/steam_remap.rs"]
 pub mod steam_remap;
 /// Linux: virtual Steam Deck over **USB/IP** (`vhci_hcd`) — the shippable, Secure-Boot-clean,