feat(host/windows): ViGEm virtual gamepad backend

Windows GamepadManager via vigem-client (ViGEmBus) — the uinput-xpad analogue: one virtual Xbox 360 controller per client pad index, created lazily on first State. GameStream/Moonlight already uses the XInput conventions (low-16 button bits, sticks -32768..32767 +Y up, triggers 0..255), so the GamepadFrame->XGamepad mapping is 1:1. Replaces the non-Linux GamepadManager stub (same new/handle/pump_rumble API the m3 PadBackend drives, so no m3 change). Graceful when ViGEmBus is absent (gamepad disabled, session continues). Compiles clean on Windows + Linux; live-test needs the ViGEmBus driver + a physical pad. Rumble back-channel is a TODO (ViGEm notification API).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/inject/gamepad_windows.rs

@@ -0,0 +1,70 @@
+//! Windows virtual gamepad via ViGEmBus — the analogue of the Linux uinput Xbox-360 pad.
+//! One virtual Xbox 360 controller per client pad index. GameStream/Moonlight already uses the
+//! XInput button/stick/trigger conventions (low 16 button bits, sticks −32768..32767 +Y up,
+//! triggers 0..255), so the mapping is ~1:1.
+//!
+//! Needs the ViGEmBus driver installed (like SudoVDA for the display); absent → gamepad is disabled
+//! and the session continues without it. Rumble back-channel: TODO (ViGEm notification API).
+
+use crate::gamestream::gamepad::GamepadEvent;
+use std::collections::HashMap;
+use std::sync::Arc;
+use vigem_client::{Client, TargetId, XButtons, XGamepad, Xbox360Wired};
+
+pub struct GamepadManager {
+    client: Option<Arc<Client>>,
+    pads: HashMap<u8, Xbox360Wired<Arc<Client>>>,
+}
+
+impl GamepadManager {
+    pub fn new() -> GamepadManager {
+        let client = match Client::connect() {
+            Ok(c) => {
+                tracing::info!("ViGEmBus connected (virtual Xbox 360 gamepads)");
+                Some(Arc::new(c))
+            }
+            Err(e) => {
+                tracing::warn!(
+                    error = format!("{e:?}"),
+                    "ViGEmBus unavailable — gamepad disabled (install ViGEmBus)"
+                );
+                None
+            }
+        };
+        GamepadManager {
+            client,
+            pads: HashMap::new(),
+        }
+    }
+
+    pub fn handle(&mut self, ev: &GamepadEvent) {
+        let Some(client) = self.client.clone() else {
+            return;
+        };
+        let GamepadEvent::State(f) = ev else {
+            return; // Arrival metadata — the pad is created lazily on the first State
+        };
+        let target = self.pads.entry(f.index.max(0) as u8).or_insert_with(|| {
+            let mut t = Xbox360Wired::new(client, TargetId::XBOX360_WIRED);
+            let _ = t.plugin();
+            let _ = t.wait_ready();
+            t
+        });
+        let gp = XGamepad {
+            buttons: XButtons {
+                raw: (f.buttons & 0xffff) as u16,
+            },
+            left_trigger: f.left_trigger,
+            right_trigger: f.right_trigger,
+            thumb_lx: f.ls_x,
+            thumb_ly: f.ls_y,
+            thumb_rx: f.rs_x,
+            thumb_ry: f.rs_y,
+        };
+        let _ = target.update(&gp);
+    }
+
+    pub fn pump_rumble(&mut self, _send: impl FnMut(u16, u16, u16)) {
+        // TODO: wire the ViGEm rumble notification back-channel (Xbox360Wired::request_notification).
+    }
+}