feat(win): one D3D12 DP per screen — create_dp_d3d12_for_screen + D3D12 present origin (multi-screen M6)

[dfattal]

Depends on

DisplayXR/displayxr-runtime#1879 (appends xrt_plugin_iface::create_dp_d3d12_for_screen and xrt_display_processor_d3d12::set_present_origin, ABI unchanged at 5) — shipped in runtime v2.33.0. This branch is rebased on main after #333 (Windows pin → v2.33.0) and #334 (Linux pin), so CI now compiles the new D3D12 paths (XRT_PLUGIN_IFACE_HAS_CREATE_DP_D3D12_FOR_SCREEN / XRT_DP_D3D12_HAS_PRESENT_ORIGIN are defined) instead of compiling them out.

What

The D3D12 twin of the D3D11 per-screen DP (e58d56e / a786eee / b44a454), for the in-process D3D12 compositor the Unity display provider runs on:

• leiasr_d3d12_create_for_screen + leiasr_d3d12_set_present_origin (leia_sr_d3d12.{h,cpp}), on the shared plan in leia_sr_multi_win.h: EXTERNAL routing (+ KEEP_DRAG_SNAP only with a real window) + display binding chained on the DX12 weaver create-info with the bind-then-routing fallback; the runtime's active display read at create; a weaver bound to a non-active display with no tracker of its own (SR D4 off) skips srInitialize and pins the nominal viewer; SR D3 bound lens per screen, disabled before destroy; per weave, a windowless EXTERNAL weaver gets srWeaverSetPresentOrigin and a pinned one srWeaverSetSimulatedViewer again (one-shot log of the first pinned weave's eye pair). The unbound create is byte-for-byte the old one (one shared impl).
• leia_dp_factory_d3d12_for_screen (leia_display_processor_d3d12.{h,cpp}): binding → SR display id (the binding's own, else leia_win_claims_lookup), DP around the per-screen weaver; the vtable/state setup both D3D12 factories share moves into leia_dp_d3d12_init; set_present_origin (slot 24) forwards to the weaver.
• Registered in leia_plugin.c under XRT_PLUGIN_IFACE_HAS_CREATE_DP_D3D12_FOR_SCREEN.
• New: get_screen_status (runtime ADR-051 D2, appended after create_dp_d3d12_for_screen in v2.33.0), passive only: ready = cached platform state READY, verified = the claim's SR FPC_VERIFIED match, serial = its FPC serial, tracker UNSUPPORTED, lens UNKNOWN, no model, no warnings, no dashboard_command. It reads only the claim table and the lock-free platform state: no SR handle, no SR SDK call, no probe. change_counter = claim-set generation (bumped by leia_win_claims_store only when the stored set actually differs) combined with the platform state. Guarded by XRT_PLUGIN_IFACE_HAS_GET_SCREEN_STATUS.

Canvas confinement needs nothing new on this arm: process_atlas already hands the weaver viewport + scissor = canvas and sets both on the command list (leiasr_d3d12_weave). SR SDK pins untouched. D3D12 late latching stays off (unchanged).

Tests

• Rebased cleanly on origin/main (no conflicts); origin/main..HEAD = this PR's 3 commits only.
• Local Windows build, scripts\build-windows.bat build (fresh build dir), against the runtime checkout at exactly v2.33.0 (b47fc4277, clean, unchanged before/after the build): exit 0. leia_plugin.c.obj references leia_dp_factory_d3d12_for_screen and leia_plugin_get_screen_status, and the DLL carries the Leia D3D12 per-screen DP strings, so both #ifdef branches are active. No new compiler warnings from plug-in sources.
• No host-testable logic changed in the D3D12 path (the plan in leia_sr_multi_win.h is reused as-is; test_sr_multi_win runs on the Linux CI).
• Rig check pending (supervisor). Rig recipe is on runtime#1879; the plug-in-side lines to look for: Leia D3D12 per-screen DP: monitor 0x… -> SR display 0x…, SR D3D12 per-screen weaver: display 0x…, window 0000000000000000, caps{…} -> plan{external=1 …}, SR D3D12 weaver created via the v2 C API (EXTERNAL routing, display bound) [windowless: phase from the present origin], and on a non-active panel … simulated nominal viewer PINNED … then first weave with the pinned viewer — predicted eyes … (PAIR — weaving). displayxr-cli status should show a leia-sr vendor cell per claimed screen (ready / verified / FPC serial).

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