feat(host/windows,drivers): gamepad driver attach/heartbeat health surfaced in logs

The gamepad drivers have no IOCTL plane (hidclass gates the stack), so
until now the host had ZERO visibility into whether a driver ever
bound: a pad could be "created" with no driver installed and nothing
was logged. Two health fields are carved from reserved shm space
(layout-compatible; pf-driver-proto pins the offsets): driver_proto —
stamped by pf-xusb at device add + per serviced XInput IOCTL (movement
= the game-visible path) and by pf-dualsense/DS4 from its ~125Hz timer
— and driver_heartbeat. Host-side, every pad owns a DriverAttach
watcher fed from the existing service() poll: INFO on attach (WARN on
proto mismatch), and after 3s of silence ONE diagnosis WARN combining
a cached pnputil /enum-drivers store check, the devnode's CM problem
code (CM_Locate_DevNodeW/CM_Get_DevNode_Status on the instance id now
captured from the create callback, with plain-language hints: 28 = not
installed, 52 = signature/Memory Integrity, …) and the driver's debug
log path. Also fixes a real bug both SwDeviceCreate wrappers shared:
the 10s WaitForSingleObject result was ignored and the callback
HRESULT zero-initialised, so a PnP timeout read as SUCCESS (now E_FAIL
init + explicit timeout error). Failure-mode table:
design/gamepad-driver-health.md.

Linux workspace green; Windows host + drivers CI-compile only, on-box
recipe at the bottom of the design doc.

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

crates/punktfunk-host/src/encode/windows/nvenc.rs

@@ -1174,17 +1174,13 @@ impl Encoder for NvencD3d11Encoder {
         // the oldest ready AU. `None` = nothing completed yet — the session loop keeps the frame
         // in flight and re-polls next tick, capture never blocks on the WDDM scheduling wait.
         if self.async_rt.is_some() {
-            loop {
-                let done = match self
-                    .async_rt
-                    .as_mut()
-                    .expect("checked just above")
-                    .done_rx
-                    .try_recv()
-                {
-                    Ok(d) => d,
-                    Err(_) => break,
-                };
+            while let Ok(done) = self
+                .async_rt
+                .as_mut()
+                .expect("checked just above")
+                .done_rx
+                .try_recv()
+            {
                 self.absorb_done(done)?;
             }
             return Ok(self