feat(gamepad): Windows Steam Deck backend — Steam-Input-promoted UMDF virtual Deck

The N4 GO verdict, productized. GamepadPref::SteamDeck on a Windows host
now builds a real virtual Deck instead of folding to DualSense: games
get native Deck glyphs + both trackpads + gyro + all four back grips
through Steam Input's own remapping.

- steam_deck_windows.rs: DeckWinPad/DeckWinProto/SteamDeckWindowsManager
  over the sealed shm channel, sharing the whole Linux Deck codec
  (steam_proto now compiles on Windows too — it was already pure). The
  SwDevice identity carries usb_mi: Some(2): the &MI_02 hardware-id
  token hidclass mirrors into the HID child and Steam parses as the
  wired controller interface — the promotion gate.
- Driver: DEVTYPE_STEAMDECK (3) graduates from the spike — SET_FEATURE
  0xEB rumble / 0x8F haptic pulses are republished to the host through
  the output slot (report-id-0 prefixed, so parse_steam_output sees the
  Linux wire shape), and the 0xAE/GET_STRING serial + 0x83 unit id are
  per-pad (read from the section's pad_index; PFDK<unit-id> matches
  steam_proto::deck_serial).
- Router: SteamDeck arms in the Windows Pads paths; pick_gamepad flips
  SteamDeck-if-windows -> SteamDeck (the DualSense fold retires);
  dualsense-windows-test grows --deck.

ON-GLASS VALIDATED on .173 (rebuilt signed driver 9.9.0714.12xx
installed, Steam live): the manager-created pad (index 1) enumerates
with per-pad serial PFDK50460001, Steam logs Interface: 2 ->
'!! Steam controller device opened' -> 'Steam Controller reserving
XInput slot 0' -> PollState 2 (actively polling our cycling input
frames) -> mapping activated; clean teardown on exit. Rumble round-trip
through a real game remains an on-glass debt (nothing sent 0xEB during
the idle hold).

Known gap vs Linux: no physical-Steam-controller conflict degrade on
Windows yet (degrade_steam_on_conflict is Linux-only — /sys scan); a
Windows equivalent needs SetupDi enumeration and is deferred.

Verified: .21 clippy -D warnings + 304/0 tests + fmt --all; .133 clippy
-D warnings + the WDK driver-workspace check.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/punktfunk-host/src/inject.rs

@@ -527,6 +527,11 @@ pub mod pad_slots;
 #[cfg(target_os = "linux")]
 #[path = "inject/linux/steam_controller.rs"]
 pub mod steam_controller;
+/// Windows: virtual Steam Deck via the same UMDF minidriver + shared-memory channel
+/// (device-type 3) — promoted by Steam Input thanks to the `&MI_02` hardware-id synthesis.
+#[cfg(target_os = "windows")]
+#[path = "inject/windows/steam_deck_windows.rs"]
+pub mod steam_deck_windows;
 /// Linux: virtual Steam Deck via the USB gadget subsystem (`raw_gadget` + `dummy_hcd`) — the only
 /// virtual-Deck transport Steam Input promotes (presents the controller on USB interface 2).
 /// SteamOS-host only (needs `dummy_hcd` + `raw_gadget`).
@@ -534,8 +539,9 @@ pub mod steam_controller;
 #[path = "inject/linux/steam_gadget.rs"]
 pub mod steam_gadget;
 /// Transport-independent Steam Controller / Steam Deck HID contract (descriptor, byte-exact Deck
-/// serializer, XInput/rich mappers, rumble parser), used by the Linux UHID backend ([`steam_controller`]).
-#[cfg(target_os = "linux")]
+/// serializer, XInput/rich mappers, rumble parser), used by the Linux UHID backend
+/// ([`steam_controller`]) and the Windows UMDF backend ([`steam_deck_windows`]).
+#[cfg(any(target_os = "linux", target_os = "windows"))]
 #[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.