feat(gamepad): N4 spike kit — software-devnode Steam Deck probe for Windows

The gamepad-new-types §6 go/no-go rig, ready to run the moment .173 is
back (the box is currently down, so the observation itself is still
owed): does Steam Input on Windows promote a software-devnode HID Deck
(28DE:1205), or does it need a real USB bus identity (the documented
GameInput instance-path gap — the Linux 'Interface: -1' lesson)?

- Driver: scratch device_type=3 serves the Deck identity — the captured
  38-byte controller-interface descriptor, 28DE:1205 attributes, Valve
  strings, the Deck neutral frame, and the Steam 0x83/0xAE feature
  contract (SET_FEATURE latches the command, GET_FEATURE answers it —
  attribute blob + unit serial mirroring steam_proto::feature_reply).
  Never stamped by a session. INF gains pf_steamdeck.
- Host: deck_spike_hold() + the `deck-windows-spike` subcommand — stamps
  devtype 3, spawns the devnode under VID_28DE&PID_1205, streams the
  neutral frame, prints what to observe (Steam logs/controller.txt,
  controller settings) and logs any output reports Steam writes.

Run recipe (on .173, once the updated signed driver is staged): install
driver, start Steam, `punktfunk-host.exe deck-windows-spike`, watch
controller.txt. GO -> plan a proper N4 phase (the Deck codec is already
shared); NO-GO -> document next to the Linux Interface:-1 note and keep
the SteamDeck->DualSense Windows fold.

Verified: .133 clippy -D warnings + the driver workspace cargo check
(WDK) both green; .21 clippy + 304/0 tests unaffected.

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

crates/pf-driver-proto/src/lib.rs

@@ -538,6 +538,10 @@ pub mod gamepad {
     /// `device_type` = DualSense Edge (`VID_054C&PID_0DF2` HID identity — the DualSense report
     /// codec plus the four native back/Fn button bits).
     pub const DEVTYPE_DUALSENSE_EDGE: u8 = 2;
+    /// `device_type` = **N4-spike** Steam Deck identity (`VID_28DE&PID_1205`). Exists only for
+    /// the `deck-windows-spike` go/no-go probe (does Steam Input on Windows promote a
+    /// software-devnode HID Deck?) — never stamped by a session.
+    pub const DEVTYPE_STEAMDECK_SPIKE: u8 = 3;
 
     /// The value a gamepad driver writes into its section's `driver_proto` field once it attaches —
     /// the host's positive "driver is alive on this section" signal (health check + version audit).