v0.4.0: Direct3D 11/12 backends, in-game renderer selection, per-run logging

- ra3.dx: D3D11 and D3D12 presentation backends (runtime HLSL via d3dcompiler);
  2D image blit and the GPU heightfield terrain raymarch, with the corner
  minimap/FPS overlays. Non-Windows builds link a null fallback.
- ra3.display: preferred backend plus ordered fallback (Vulkan/D3D11/D3D12/SDL);
  menu gains a Renderer option and the CLI gains --dx11/--dx12/--sdl, which the
  render command now honours too.
- vendor libenderlog (MIT): every run writes openra3.log next to the exe and
  archives the previous run's log; records at warn and above carry a call stack
  (native fallback, since libc++ has no <stacktrace>).
- Windows crash reporter writes openra3_crash.log (faulting module + backtrace);
  D3D/DXGI diagnostics are routed through the logger.

third_party/libenderlog/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 EnderTheCoder
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.