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-core/src/abi.rs

@@ -885,9 +885,9 @@ pub const PUNKTFUNK_GAMEPAD_DUALSHOCK4: u32 = 4;
 /// UHID classic Steam Controller (Valve `28DE:1102`, kernel `hid-steam`): one stick + dual
 /// trackpads + two grip paddles. Honored only where available (Linux hosts); else Xbox 360.
 pub const PUNKTFUNK_GAMEPAD_STEAMCONTROLLER: u32 = 5;
-/// UHID Steam Deck controller (Valve `28DE:1205`, kernel `hid-steam`): full Deck gamepad incl. the
-/// four back grips, a right trackpad, and the IMU; re-grabbed by Steam Input with native glyphs when
-/// Steam runs on the host. Honored only where available (Linux hosts); else folds to X-Box 360.
+/// Steam Deck controller (Valve `28DE:1205`): full Deck gamepad incl. the four back grips, both
+/// trackpads, and the IMU; re-grabbed by Steam Input with native glyphs when Steam runs on the
+/// host. Honored on Linux AND Windows hosts; else folds to X-Box 360.
 pub const PUNKTFUNK_GAMEPAD_STEAMDECK: u32 = 6;
 /// DualSense Edge (Sony `054C:0DF2`): the DualSense plus two back buttons + two Fn buttons, so a
 /// client's back paddles land on native slots. Folds to `DUALSENSE` until its backend lands.

crates/punktfunk-core/src/config.rs

@@ -160,9 +160,10 @@ pub enum GamepadPref {
     /// trackpads + two grip paddles. The wire right stick drives the right pad; a left-pad contact
     /// shadows the stick (hardware multiplex). Needs Linux UHID.
     SteamController,
-    /// UHID Steam Deck controller (Valve `28DE:1205`, kernel `hid-steam`) — full Deck gamepad incl.
-    /// the four back grips (L4/L5/R4/R5), a right trackpad, and the IMU; re-grabbed by Steam Input
-    /// with native glyphs when Steam runs on the host. Needs Linux UHID.
+    /// Steam Deck controller (Valve `28DE:1205`) — full Deck gamepad incl. the four back grips
+    /// (L4/L5/R4/R5), both trackpads, and the IMU; re-grabbed by Steam Input with native glyphs
+    /// when Steam runs on the host. Linux (kernel `hid-steam` via UHID/usbip/gadget) or Windows
+    /// (UMDF minidriver, Steam-Input-promoted).
     SteamDeck,
     /// DualSense Edge (Sony `054C:0DF2`, kernel `hid-playstation` ≥ 6.3 / Windows UMDF) — the
     /// DualSense plus two back buttons + two Fn buttons, so a client's back paddles (Deck grips,