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.

src/test/tests/test_door_and_flashlight.gd

@@ -43,8 +43,11 @@ func test_flashlight_aims_a_tight_forward_spot() -> bool:
 	var c := TestUtils.check(lamp != null and lamp.spot_angle <= 20.0,
 		"flashlight cone is narrow enough to read as a torch")
 	var d := TestUtils.check(lamp != null and not lamp.visible, "flashlight starts off")
+	var e := TestUtils.check(lamp != null
+		and is_zero_approx(lamp.light_volumetric_fog_energy),
+		"headless/compatibility builds leave the flashlight non-volumetric")
 	root.free()
-	return a and b and c and d
+	return a and b and c and d and e
 
 func test_flashlight_widens_perception() -> bool:
 	## Without the flashlight, an NPC at AWARE_RADIUS + 3 m is unaware.

src/test/tests/test_materials.gd

@@ -77,14 +77,19 @@ func test_environment_tuning_applies_phase_values() -> bool:
 	var f := TestUtils.check(
 		env.fog_light_color.is_equal_approx(late["fog_color"]),
 		"phase fog colour is used")
-	return a and b and c and d and e and f
+	var advanced := Materials.forward_plus_active()
+	var g := TestUtils.check(env.volumetric_fog_enabled == advanced,
+		"volumetric fog is gated to Forward+ (advanced=%s)" % advanced)
+	var h := TestUtils.check(env.sdfgi_enabled == advanced,
+		"SDFGI is gated to Forward+ (advanced=%s)" % advanced)
+	return a and b and c and d and e and f and g and h
 
 func test_every_phase_has_environment_keys() -> bool:
 	var ok := true
 	for phase in [Rules.Phase.EARLY, Rules.Phase.MIDDAY, Rules.Phase.EVENING, Rules.Phase.LATE]:
 		var cfg: Dictionary = GameManager.PHASE_LIGHTING.get(phase, {})
 		for key in ["exposure", "glow", "fog_color", "fog_density", "fog_energy",
-				"contrast", "saturation"]:
+				"contrast", "saturation", "volumetric_density", "volumetric_energy"]:
 			if not cfg.has(key):
 				ok = false
 	return TestUtils.check(ok, "all phases set exposure/glow/fog/grading")