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.

DONE.md

@@ -1279,3 +1279,35 @@ have no stage in the committed `docs/screenshots/` gallery, only in `capture_rea
       0 bad**; the new screenshots are 18.2 / 32.6 MAE against their references.
 - [-] Update `docs/architecture.md` (venue geometry), `README.md` (gallery) and the screenshot
       table when the stages land.
+
+## Forward+ desktop preset and a volumetric flashlight (v0.7.1)
+
+Completed 2026-11-01. The optional Desktop HQ build uses Forward+ with volumetric fog, SDFGI and a volumetric flashlight; Compatibility/Web/headless remain the default. The entrance A/B improved the metric gap 1.568 → 1.187. The vision-judge retry remains tracked separately because the API key was invalid.
+
+The Compatibility renderer has no volumetrics, so the flashlight is a tight pool of light with
+no visible shaft. A second desktop build can render it properly without touching the CI/default
+path.
+
+- [x] Write the preset as an `override.cfg` (Godot reads it beside the binary/project) that sets
+      `rendering/renderer/rendering_method="forward_plus"`, enables `volumetric_fog_*` and SDFGI,
+      and keeps the Compatibility build as the default (`project.godot` unchanged). The preset
+      lives in `packaging/desktop_hq/`; `local lights adapted for Godot 4.7 falloff` too.
+- [x] Gate the effect in code: only give the flashlight a volumetric component when the renderer
+      is Forward+ (`RenderingServer.get_rendering_device() != null`), so Web/CI builds are
+      untouched and the existing headless tests keep passing. Environment volumetric fog/SDFGI
+      use the same gate; tests assert the headless lamp is non-volumetric.
+- [x] Tune `light_volumetric_fog_energy`/`fog_density` for the LATE phase and re-check the
+      entrance so the shaft does not wash the facade again. LATE density is 0.020 and the lamp
+      volumetric energy is 3.0; the entrance read improves without bleaching the brick.
+- [x] A/B the two renderers with `capture_realism.gd` (`--stages=late --flashlight`, two `--out`
+      dirs) and record the diff in `docs/screens/realism/2026-11-01-forward-plus/`: entrance
+      metric gap 1.568 → 1.187, two-shot mean 0.907 → 0.723. Judge scores are blocked by the
+      invalid API key and tracked with the other judge retry.
+- [x] Add the preset to `tools/build_releases.sh` and `docs/RELEASING.md` as an optional
+      "desktop HQ" artifact, and note the runtime requirement (Vulkan driver) in `README.md`.
+      `gig-line-desktop-hq-<version>.zip` packages the Linux/Windows binaries, override.cfg and
+      README; `publish_release.sh` uploads it when present.
+- [x] Test: a headless run must still boot when Forward+ is unavailable (the preset must degrade
+      to Compatibility instead of failing to start). Verified with the preset in the project
+      root: `godot --headless --path . --quit-after 5` exits 0 and starts the game; an exported
+      HQ binary also boots with Vulkan Forward+ under Xvfb.