fix(windows-client): clear clippy -D warnings on MSVC

The cfg(windows) code can't be lint-checked on the Linux dev box, so three
-D warnings slipped through (caught by windows.yml; the FFI + shaders compiled
fine):
- gpu.rs: SetMultithreadProtected returns a must-use BOOL -> `let _ =`.
- video.rs: drop the unused GpuFrame::ten_bit field (present keys off `hdr`;
  the value is still computed locally for the first-frame log).
- present.rs: GpuView::frame is an RAII keep-alive (its Drop returns the decoder
  surface to the pool), never read -> #[allow(dead_code)].

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

clients/windows/src/gpu.rs

@@ -97,7 +97,9 @@ fn create_device() -> Result<SharedDevice> {
             // FFmpeg also sets this during hwdevice init, but doing it up front keeps the
             // cross-thread `Send`/`Sync` sound from the moment the device exists.
             if let Ok(mt) = context.cast::<ID3D11Multithread>() {
-                unsafe { mt.SetMultithreadProtected(true) };
+                unsafe {
+                    let _ = mt.SetMultithreadProtected(true); // returns the prior state; ignore
+                }
             }
             tracing::info!(
                 driver = if hardware {

clients/windows/src/present.rs

@@ -82,6 +82,8 @@ float4 ps_p010(VSOut i) : SV_Target {
 struct GpuView {
     y: ID3D11ShaderResourceView,
     c: ID3D11ShaderResourceView,
+    /// Held only for its `Drop` (returns the decoder surface to the reuse pool) — never read.
+    #[allow(dead_code)]
     frame: GpuFrame,
 }
 

clients/windows/src/video.rs

@@ -91,11 +91,9 @@ pub struct GpuFrame {
     pub height: u32,
     /// Texture-array slice this frame occupies (`AVFrame::data[1]`).
     pub index: u32,
-    /// BT.2020 PQ HDR10 (P010, ST.2084) vs ordinary 8-bit BT.709 SDR (NV12).
+    /// BT.2020 PQ HDR10 (P010, ST.2084) vs ordinary 8-bit BT.709 SDR (NV12). The present path keys
+    /// SRV format + shader off this (the host couples 10-bit ⟺ HDR).
     pub hdr: bool,
-    /// 10-bit (P010, R16 planes) vs 8-bit (NV12, R8 planes) — kept for the first-frame log; the
-    /// present path keys colour/format off `hdr` (the host couples 10-bit ⟺ HDR).
-    pub ten_bit: bool,
     guard: D3d11FrameGuard,
 }
 
@@ -472,7 +470,6 @@ impl D3d11vaDecoder {
                 height: (*self.frame).height as u32,
                 index: (*self.frame).data[1] as usize as u32,
                 hdr,
-                ten_bit,
                 guard: D3d11FrameGuard(cloned),
             };
             log_layout_once(frame.width, frame.height, frame.index, hdr, ten_bit);