Add the optional Forward+ desktop HQ build

Package a Forward+ preset with volumetric fog, SDFGI and a volumetric flashlight
for a separate Linux/Windows Desktop HQ zip. Gate the effects on a real
RenderingDevice, tune LATE fog, and adapt local light falloff for Godot 4.7.
Record the Compatibility/Forward+ A/B captures and metrics, add the artifact to
the build/publish scripts, and keep the default Compatibility/Web path
unchanged. Headless 231/231, Python 87/87; exported HQ binary boots with Vulkan.

packaging/desktop_hq/README.txt

@@ -0,0 +1,16 @@
+Gig Line — Desktop HQ build
+===========================
+
+This build uses Godot's Forward+ renderer instead of the default
+GL Compatibility renderer, enabling volumetric fog and SDFGI.
+
+Requirements:
+- A Vulkan-capable GPU/driver (Linux or Windows).
+- Keep override.cfg next to the executable. Without it the binary falls back
+  to the normal Compatibility build.
+
+The game still runs if Forward+ is unavailable, but the desktop-only effects
+will be disabled.
+
+Linux:   chmod +x gig-line-linux-*.x86_64 && ./gig-line-linux-*.x86_64
+Windows: run gig-line-windows-*.exe