feat(gamepad): Switch Pro backend — Linux UHID via hid-nintendo (N2)

A virtual Pro Controller (057E:2009, BUS_USB, verbatim 203-byte USB
descriptor triple-cross-checked from real-device captures) bound by
hid-nintendo (>= 5.16): Nintendo-family client pads get correct glyphs +
POSITIONAL layout (wire south/east/west/north -> Switch B/A/Y/X, so the
physical-position <-> glyph relationship survives), live gyro/accel, and
HD-rumble feedback — instead of folding to Xbox360 (mirrored A/B + X/Y,
no motion).

- switch_proto: report-0x30/0x21/0x81 codec + the entire canned probe
  conversation, pinned line-by-line against hid-nintendo.c: 0x80-family
  USB acks, device info (type 0x03 + per-pad MAC), SPI-flash calibration
  blobs (user magics ABSENT -> factory path; sticks 2048 +/- 1400 with
  the left/right byte-order difference; IMU offsets 0 + the driver's own
  default scales so raw units pass 1:1), rumble amplitude decode through
  the driver's inverted joycon_rumble_amplitudes table, player lights ->
  0xCD PlayerLeds. 11 new pin tests.
- switch_pro: UHID backend answering the probe from the manager's
  service pass; SwitchProManager = UhidManager<SwitchProProto> (the 8 ms
  heartbeat doubles as the steady 0x30 stream the driver's post-probe
  rate limiter wants). switchpro-test CLI smoke.
- Router/fold: SwitchPro arms; pick_gamepad SwitchPro -> itself on Linux;
  degrade_if_no_uhid covers it. SDL picker: NintendoSwitchPro + JoyconPair
  declare SwitchPro.

Headless-validated on .21 (hid-nintendo 7.1): probe completes ('using
factory cal' for sticks + IMU, player-1 LED round-trips to the 0xCD
plane), gamepad + IMU input devices created, and an evdev capture pins
the positional swap (wire A/B -> BTN_SOUTH/BTN_EAST) + full-range stick
scaling. .21 clippy -D warnings + 303/0 tests; .133 clippy -D warnings.

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

crates/punktfunk-host/src/inject.rs

@@ -527,6 +527,15 @@ pub mod pad_slots;
 #[cfg(target_os = "linux")]
 #[path = "inject/linux/steam_controller.rs"]
 pub mod steam_controller;
+/// Linux: virtual Nintendo Switch Pro Controller via UHID (kernel `hid-nintendo`).
+#[cfg(target_os = "linux")]
+#[path = "inject/linux/switch_pro.rs"]
+pub mod switch_pro;
+/// Transport-independent Switch Pro Controller codec + the canned `hid-nintendo` handshake
+/// replies, used by the Linux UHID backend ([`switch_pro`]).
+#[cfg(target_os = "linux")]
+#[path = "inject/proto/switch_proto.rs"]
+pub mod switch_proto;
 /// 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`).