Fix #378: draw on the GPU that drives the primary display on Windows (#631)

* Fix #378: draw on the GPU that drives the primary display on Windows

The low-power preference picked the AMD Ryzen integrated GPU on a desktop
whose monitors all hang off an NVIDIA card. Presenting from the headless
iGPU to a window on another GPU took the AMD display driver down, blacking
out every monitor for two minutes before PdfCraft exited.

Windows now gets the display-aware adapter choice Linux already had:
EnumDisplayDevices (through the safe `winsafe` crate, MIT) says which
adapter drives each desktop display and which is primary; `pick_adapter`
matches that to the wgpu adapters by PCI ids. The GPU driving the primary
display wins, as the built-in panel does on Linux (#8). The log names the
GPU chosen, the first question when a window stays black.

Synthetic tests cover the Windows device-id parser and the primary-display
rule; a live test checks the enumeration on the running machine. Verified
on a Ryzen 7000 + RTX 3090 desktop: the app now starts on the 3090.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01XBMGuLLMhs1h8orSxcJXER

* 631: the winsafe feature comment says user (and kernel)

---------

Co-authored-by: Claude Fable 5.1 <[email protected]>
Co-authored-by: Brandon Thomas <[email protected]>

docs/development.md

@@ -58,7 +58,7 @@ OpenGL can't start either, PdfCraft exits with both errors in the log. The fallb
 | `RUST_LOG` | Log levels for standard error and the log file (see [Logs](#logs)) |
 | `RUST_BACKTRACE` | `1` adds a backtrace to the report of an internal error |
 | `XDG_DATA_HOME` | Linux/FreeBSD: base of the settings folder (`pdfcraft/`), the log folder and crash recovery |
-| `WGPU_POWER_PREF` | GPU choice; by default PdfCraft prefers the low-power (integrated) GPU |
+| `WGPU_POWER_PREF` | GPU choice; by default PdfCraft draws on the GPU that drives the primary display (Windows) or the built-in panel (Linux), else the low-power (integrated) GPU. The log says which one was chosen |
 | `WGPU_BACKEND` | Graphics backend; by default Windows uses Direct3D 12, falling back to OpenGL |
 | `PDFCRAFT_RENDERER` | `gl` starts with OpenGL (glow) and never loads wgpu; `wgpu` reports a wgpu failure instead of retrying with OpenGL; unset, wgpu is retried with OpenGL when it can't start (see [Renderer fallback](#renderer-fallback)) |
 | `CRAFT_FONTS_DIR` | Build time: a [craft-fonts](https://github.com/storytold/craft-fonts) checkout to embed (Japanese fonts) |