feat(windows-drivers): STEP 4 (2/n) — create_monitor + real mode DDIs + ADD/REMOVE

The virtual-monitor lifecycle is now code-complete on the driver side (CI-green;
deployed — no load/adapter-init regression, Status=OK):

- new monitor.rs: the monitor/mode model (Mode/MonitorObject/MONITOR_MODES), ported from
  upstream virtual-display-rs with guid:u128 -> session_id:u64. create_monitor builds an
  EDID (serial=id) -> IddCxMonitorCreate -> IddCxMonitorArrival, stores the monitor, and
  returns the OS target id + adapter LUID for AddReply. remove_monitor / clear_all depart
  + drop. display_info/target_mode build the DISPLAYCONFIG timing (the union videoStandard
  u32 set directly — bindgen-API-agnostic, vs the oracle new_bitfield_1 transmute).
- callbacks.rs: parse_monitor_description (EDID-serial lookup -> count-then-fill
  IDDCX_MONITOR_MODE) + monitor_query_modes (pointer-match -> IDDCX_TARGET_MODE) are real.
- control.rs: IOCTL_ADD -> create_monitor + AddReply, REMOVE -> remove_monitor, CLEAR_ALL
  -> clear_all, via read_input/write_output_complete WDF buffer helpers. SET_RENDER_ADAPTER
  still stubbed (hybrid-GPU pin, next) + the watchdog thread (next).
- DISPLAYCONFIG_* resolve at the wdk_sys root (pub use types::*), not iddcx.

Warnings are the STEP-7 *2/HDR stubs + created_at (read by the watchdog, next). The
on-glass "monitor appears at WxH@Hz" gate awaits the host switch to pf_vdisplay_proto.

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

packaging/windows/drivers/pf-vdisplay/src/adapter.rs

@@ -120,3 +120,9 @@ pub fn init_adapter(device: WDFDEVICE) -> NTSTATUS {
 pub fn set_adapter(adapter: iddcx::IDDCX_ADAPTER) {
     let _ = ADAPTER.set(SendAdapter(adapter));
 }
+
+/// The created adapter handle, once `EvtIddCxAdapterInitFinished` has fired — for `create_monitor`
+/// (`IddCxMonitorCreate`) and SET_RENDER_ADAPTER. `None` before adapter init completes.
+pub(crate) fn adapter() -> Option<iddcx::IDDCX_ADAPTER> {
+    ADAPTER.get().map(|a| a.0)
+}