feat(inject): generic PadProto + UhidManager<B> stateful manager (3.3 layer 2)

The shared skeleton of the five stateful UHID/UMDF managers (Linux
DualSense / DualShock 4 / Steam Deck, Windows DualSense / DualShock 4),
written once over PadSlots: event routing with the unplug sweep and
was-the-unplug early return, the merge-preserving frame fold, rich-input
application, the silence heartbeat (with a backend force hook for the
Steam mode-entry pulse), and the feedback pump with rumble dedup +
HidoutDedup. A backend supplies only its per-controller half via
PadProto: open / neutral / merge_frame / apply_rich / write_state /
service — exactly where the real protocol differences live.

Method surface (new/handle/apply_rich/pump/heartbeat) matches what the
punktfunk1.rs Pads router already drives, so each backend will convert
as a pub type alias with zero router edits.

Additive only — no backend converted yet. 8 mock-backend tests make the
manager lifecycle unit-testable for the first time; G2 (rich fields
survive a button-only frame) and G10 (Arrival eager-creates) are now
generic regression tests, plus removal-frame no-recreate, absent-pad
rich drop, create-backoff state tracking, rumble/hidout dedup + re-arm
on recreate, and heartbeat gap/force semantics.

Verified on .21: clippy --all-targets -D warnings clean; suite 293
pass / 0 fail (285 prior + 8 new).

Part of G12/3.3 (gamepad-review-cleanup.md §3a.3, commit 3 of the §3a.4
sequence).

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

crates/punktfunk-host/src/inject.rs

@@ -517,6 +517,12 @@ pub mod pad_gate;
 #[cfg(any(target_os = "linux", target_os = "windows"))]
 #[path = "inject/pad_slots.rs"]
 pub mod pad_slots;
+/// The generic stateful virtual-pad manager ([`uhid_manager::UhidManager`]) — event routing, frame
+/// merge, heartbeat, and feedback pump shared by the five UHID/UMDF backends; each supplies only
+/// its per-controller protocol via [`uhid_manager::PadProto`] (G12).
+#[cfg(any(target_os = "linux", target_os = "windows"))]
+#[path = "inject/uhid_manager.rs"]
+pub mod uhid_manager;
 /// Linux: virtual Steam Deck via UHID — the kernel `hid-steam` driver binds it as a real Deck.
 #[cfg(target_os = "linux")]
 #[path = "inject/linux/steam_controller.rs"]