fix(host/windows): honor the SudoVDA's real HDR state (stop wiping the user's HDR toggle)

HDR streamed nothing and "didn't persist" because build() forced the SudoVDA's
advanced-color state to match the handshake bit_depth on every build — with an
8-bit-negotiated session (the common case: clients advertise no 10-bit cap) that
meant set_advanced_color(false) on every connect, wiping a user's deliberate
Windows HDR toggle on the virtual display.

But the whole pipeline already follows the monitor's REAL HDR state: WGC captures
FP16 when HDR is on, NVENC forces Main10 + BT.2020 PQ from the 10-bit capture
format regardless of the negotiated depth (encode/nvenc.rs), and the client
auto-detects PQ from the HEVC VUI. So the negotiated bit_depth must NOT drive the
monitor's colorspace.

- build(): only ever ENABLE HDR (proactively, for a negotiated 10-bit session);
  never force it off. A user-enabled HDR session now persists and flows end-to-end.
- secure-desktop mux: gate the HDR→SDR drop (for the DDA leg) on the monitor's
  ACTUAL advanced-color state at switch time, not bit_depth — so an HDR session
  with an 8-bit handshake still drops correctly for Winlogon and restores after.
- sudovda: add advanced_color_enabled() reader (DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/punktfunk-host/src/vdisplay/sudovda.rs

@@ -23,11 +23,11 @@ use windows::Win32::Devices::DeviceAndDriverInstallation::{
 };
 use windows::Win32::Devices::Display::{
     DisplayConfigGetDeviceInfo, DisplayConfigSetDeviceInfo, GetDisplayConfigBufferSizes,
-    QueryDisplayConfig, SetDisplayConfig, DISPLAYCONFIG_DEVICE_INFO_GET_SOURCE_NAME,
-    DISPLAYCONFIG_DEVICE_INFO_SET_ADVANCED_COLOR_STATE, DISPLAYCONFIG_MODE_INFO,
-    DISPLAYCONFIG_PATH_INFO, DISPLAYCONFIG_SET_ADVANCED_COLOR_STATE,
-    DISPLAYCONFIG_SOURCE_DEVICE_NAME, QDC_ONLY_ACTIVE_PATHS, SDC_ALLOW_CHANGES, SDC_APPLY,
-    SDC_USE_SUPPLIED_DISPLAY_CONFIG,
+    QueryDisplayConfig, SetDisplayConfig, DISPLAYCONFIG_DEVICE_INFO_GET_ADVANCED_COLOR_INFO,
+    DISPLAYCONFIG_DEVICE_INFO_GET_SOURCE_NAME, DISPLAYCONFIG_DEVICE_INFO_SET_ADVANCED_COLOR_STATE,
+    DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO, DISPLAYCONFIG_MODE_INFO, DISPLAYCONFIG_PATH_INFO,
+    DISPLAYCONFIG_SET_ADVANCED_COLOR_STATE, DISPLAYCONFIG_SOURCE_DEVICE_NAME,
+    QDC_ONLY_ACTIVE_PATHS, SDC_ALLOW_CHANGES, SDC_APPLY, SDC_USE_SUPPLIED_DISPLAY_CONFIG,
 };
 use windows::Win32::Foundation::{CloseHandle, HANDLE, LUID};
 use windows::Win32::Graphics::Gdi::{
@@ -276,6 +276,48 @@ pub(crate) unsafe fn set_advanced_color(target_id: u32, enable: bool) -> bool {
     false
 }
 
+/// Read the SudoVDA target's CURRENT advanced-color (HDR) state via the CCD API — i.e. whether HDR is
+/// actually ON for the virtual display right now (e.g. because the user toggled it in Windows display
+/// settings). The capture/encode pipeline follows the monitor's real colorspace (WGC → FP16 → NVENC
+/// Main10 BT.2020 PQ), so this is the authoritative "is this an HDR session" signal — NOT the
+/// handshake-negotiated bit depth. Returns false if the target isn't found / the query fails.
+pub(crate) unsafe fn advanced_color_enabled(target_id: u32) -> bool {
+    let mut np = 0u32;
+    let mut nm = 0u32;
+    if GetDisplayConfigBufferSizes(QDC_ONLY_ACTIVE_PATHS, &mut np, &mut nm).is_err() {
+        return false;
+    }
+    let mut paths = vec![DISPLAYCONFIG_PATH_INFO::default(); np as usize];
+    let mut modes = vec![DISPLAYCONFIG_MODE_INFO::default(); nm as usize];
+    if QueryDisplayConfig(
+        QDC_ONLY_ACTIVE_PATHS,
+        &mut np,
+        paths.as_mut_ptr(),
+        &mut nm,
+        modes.as_mut_ptr(),
+        None,
+    )
+    .is_err()
+    {
+        return false;
+    }
+    for p in paths.iter().take(np as usize) {
+        if p.targetInfo.id == target_id {
+            let mut info = DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO::default();
+            info.header.r#type = DISPLAYCONFIG_DEVICE_INFO_GET_ADVANCED_COLOR_INFO;
+            info.header.size = size_of::<DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO>() as u32;
+            info.header.adapterId = p.targetInfo.adapterId;
+            info.header.id = p.targetInfo.id;
+            if DisplayConfigGetDeviceInfo(&mut info.header) == 0 {
+                // value bit 1 = advancedColorEnabled (bit 0 = advancedColorSupported).
+                return (info.Anonymous.value & 0x2) != 0;
+            }
+            return false;
+        }
+    }
+    false
+}
+
 /// Force the freshly-added SudoVDA monitor to the client's exact `WxH@Hz`. The ADD IOCTL only
 /// ADVERTISES the mode; Windows otherwise activates an IDD target at a 1280x720 default, so the
 /// ACTIVE mode (what DXGI Desktop Duplication captures) must be set explicitly. CDS_TEST first so a