feat(windows/capture): GDI cursor-shape poller — masked/monochrome cursors for the cursor channel

The M2c redesign (design/remote-desktop-sweep.md §8): the IddCx hardware-
cursor query is alpha-only by design — IDDCX_CURSOR_SHAPE_TYPE has no
monochrome value, the OS pre-converts monochrome to masked-color, and
masked-color delivery is dead code on modern builds (proven on-glass at
every ColorXorCursorSupport level). The driver keeps its hardware cursor
declared (XOR FULL) purely so DWM excludes every cursor type from the
IDD frame; the SHAPE now comes from a GDI poller in the capture host —
which runs as SYSTEM inside the interactive session, so no helper
process is needed.

CursorPoller (idd_push/cursor_poll.rs, the RustDesk/WebRTC/OBS pattern):
~60 Hz GetCursorInfo on a dedicated thread; rasterise via
CopyIcon→GetIconInfo→GetDIBits only when the HCURSOR value changes;
monochrome via the WebRTC truth table with invert pixels as opaque black
plus a white outline; AND-mask alpha for alpha-less color cursors;
CURSOR_SUPPRESSED = hidden; per-output visibility via the target's
desktop rect; per-monitor-V2 DPI awareness thread-scoped; input-desktop
reattach on failure + 2 s cadence (GetCursorInfo on a stale desktop
succeeds with stale data). Spawned iff the cursor channel was delivered;
a live poller is the sole overlay source (no serial-namespace mixing) —
the driver shm read remains as fallback if the poller dies.

Not chosen: DXGI Desktop Duplication GetFramePointerShape —
PointerPosition.Visible goes stale under injected-only input on current
Win11 (Sunshine #5293, exactly our topology), it burns one of the
session's four duplication slots, and IDD-output metadata has
conflicting field reports.

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

crates/pf-capture/Cargo.toml

@@ -43,7 +43,9 @@ windows = { version = "0.62", features = [
     "Win32_Graphics_Direct3D_Fxc",
     "Win32_Graphics_Dxgi",
     "Win32_Graphics_Dxgi_Common",
+    "Win32_Graphics_Gdi",
     "Win32_System_LibraryLoader",
+    "Win32_System_StationsAndDesktops",
     "Win32_System_Memory",
     "Win32_System_Threading",
     "Win32_UI_HiDpi",