fix(sky): A7 — correct sun-vector magnitude (ambient + sun were ~32% too bright)

Outdoor lighting was ~32% too bright (washed-out, weak shading). Live cdb on
retail (SmartBox::SetWorldAmbientLight + SkyDesc::GetLighting + LScape::sunlight,
binary matches refs/acclient.pdb) pinned it: at the SAME game time + DayGroup,
acdream's ambient COLOR matched retail exactly (the purple is correct, authored
per-time-of-day in the sky dat) but the LEVEL was 0.607 vs retail's 0.459.

level = AmbBright + 0.2·|sunVec|, both AmbBright=0.40, so acdream's |sunVec|≈1.06
vs retail's ≈0.30. Retail's LScape::sunlight read live = (0.2238, ~0, 0.00352),
magnitude 0.224 = DirBright, y≈0.

RetailSunVector had `y = cos(P)` (≈1) — the raw PRE-transform value SkyDesc::
GetLighting writes to arg5 (0x00500ac9), before LScape::set_sky_position's
world transform. acdream ported the un-transformed vector, so the y=cos(P)≈1
term inflated |sunVec| to ~1.06. That magnitude feeds BOTH the ambient boost
(SkyKeyframe.AmbientColor) AND the sun colour (SkyKeyframe.SunColor =
DirColor×|sunVec|), over-brightening the whole scene (terrain, objects, sky)
~30% and also pointing the sun the wrong way.

Fix: RetailSunVector = DirBright × (cos(P)·sin(H), cos(P)·cos(H), sin(P)) — the
world-space spherical form LScape::sunlight actually holds; |sunVec| == DirBright
for all H/P. After: acdream ambient (0.353,0.176,0.449) vs retail (0.360,0.180,
0.459) — within ~2%, user-confirmed "better outside". Sun direction also corrected
(was pointing ~North from the bad y term).

Tests updated to the cdb-verified values (the prior tests pinned the inflated
magnitude). 18/18 sky tests green. reference-retail-ambient-values memory updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.Core/World/SkyState.cs

@@ -74,22 +74,15 @@ public readonly record struct SkyKeyframe(
     /// (see <see cref="SkyStateProvider.RetailSunVector"/>).
     ///
     /// <para>
-    /// Why <c>|sunVec|</c> instead of <c>DirBright</c> directly: retail's
-    /// <c>PrimD3DRender::UpdateLightsInternal</c> at <c>0x0059b57c</c>
-    /// (decomp line 424118-424119) computes
-    /// <code>D3DLIGHT9.Diffuse.r = sunlight_color.r × sqrt(x²+y²+z²)</code>
-    /// from the sun vector <c>SkyDesc::GetLighting</c> built at
-    /// <c>0x00500ac9</c> (decomp lines 261343-261353):
-    /// <code>
-    ///   sunVec.x = sin(H) × DirBright × cos(P)
-    ///   sunVec.y = cos(P)                    // NOT scaled by DirBright
-    ///   sunVec.z = DirBright × sin(P)
-    /// </code>
-    /// Because Y is unscaled by <c>DirBright</c>, <c>|sunVec|</c> ≠
-    /// <c>DirBright</c> in general — it varies with sun pitch and heading.
-    /// Using <c>DirBright</c> alone underweighted the warm directional
-    /// term, letting the cool ambient/fog dominate ⇒ acdream rendered
-    /// blue-white at keyframes where retail looked warm-gray.
+    /// <c>|sunVec|</c> is retail's <c>D3DLIGHT9.Diffuse = DirColor × sqrt(x²+y²+z²)</c>
+    /// scaling (<c>PrimD3DRender::UpdateLightsInternal</c> 0x0059b57c, decomp
+    /// 424118-424119) of the WORLD-space sun vector (<c>LScape::sunlight</c>).
+    /// Because <see cref="SkyStateProvider.RetailSunVector"/> is now the
+    /// DirBright-scaled spherical vector (magnitude == DirBright, cdb-verified —
+    /// see that method), <c>|sunVec| == DirBright</c>, so this is effectively
+    /// <c>SunColor = DirColor × DirBright</c>. (A prior bug used the un-transformed
+    /// y=cos(P) vector ⇒ |sunVec|≈1.06 ⇒ the sun was ~4–5× too bright at dawn/dusk;
+    /// [[reference-retail-ambient-values]].)
     /// </para>
     /// </summary>
     public Vector3 SunColor => DirColor * SkyStateProvider.RetailSunVector(this).Length();
@@ -301,21 +294,35 @@ public sealed class SkyStateProvider
     }
 
     /// <summary>
-    /// Retail's raw sun vector (NOT normalized) — the same vector
-    /// <c>SkyDesc::GetLighting</c> writes at <c>0x00500ac9</c>
-    /// (decomp lines 261343, 261352, 261353):
+    /// Retail's world-space sun vector (NOT normalized): the standard
+    /// spherical-to-cartesian direction (East=x, North=y, Up=z) scaled by
+    /// <c>DirBright</c>:
     /// <code>
-    ///   sunVec.x = sin(H_rad) × DirBright × cos(P_rad)
-    ///   sunVec.y = cos(P_rad)                    // NOT scaled by DirBright
-    ///   sunVec.z = DirBright × sin(P_rad)
+    ///   sunVec.x = DirBright × cos(P) × sin(H)
+    ///   sunVec.y = DirBright × cos(P) × cos(H)
+    ///   sunVec.z = DirBright × sin(P)
     /// </code>
-    /// Y is unscaled by brightness on purpose — that's what makes
-    /// <c>|sunVec|</c> ≠ <c>DirBright</c> in general (the magnitude varies
-    /// with pitch/heading, which is the basis for retail's "sun is brighter
-    /// in some configurations than others" lighting behavior). The shader's
-    /// <c>uSunDir</c> uniform uses the NORMALIZED vector for N·L; the
-    /// magnitude feeds <see cref="SkyKeyframe.SunColor"/> intensity and
-    /// the ambient brightness boost in <see cref="SkyKeyframe.AmbientColor"/>.
+    /// so <c>|sunVec| == DirBright</c> exactly (cos²P·(sin²H+cos²H)+sin²P = 1).
+    ///
+    /// <para>
+    /// GROUNDED IN A LIVE cdb CAPTURE (2026-06-18, [[reference-retail-ambient-values]]):
+    /// retail's <c>LScape::sunlight</c> read at a dawn keyframe (H=90°, P=0.9°,
+    /// DirBright≈0.224) = <c>(0.2238, ~0, 0.00352)</c> — y≈0, magnitude 0.224 =
+    /// DirBright. That fed <c>level = 0.2·|sunlight| + ambient_level = 0.2·0.224 +
+    /// 0.40 = 0.445</c>, matching the captured <c>SetWorldAmbientLight</c> level.
+    /// </para>
+    /// <para>
+    /// PRIOR BUG: an earlier version returned <c>y = cos(P)</c> (≈1) — the raw
+    /// PRE-transform value the decomp's <c>SkyDesc::GetLighting</c> writes to its
+    /// <c>arg5</c> (0x00500ac9, before <c>LScape::set_sky_position</c>'s world
+    /// transform). Porting that un-transformed vector inflated <c>|sunVec|</c> to
+    /// ~1.06 instead of ~0.22, over-brightening BOTH the ambient boost
+    /// (<see cref="SkyKeyframe.AmbientColor"/>) AND the sun colour
+    /// (<see cref="SkyKeyframe.SunColor"/>) by ~30% vs retail. The world-space
+    /// form above is what <c>LScape::sunlight</c> actually holds at runtime.
+    /// </para>
+    /// The shader uses the NORMALIZED vector for N·L; the magnitude (= DirBright)
+    /// feeds the sun-colour intensity and the ambient brightness boost.
     /// </summary>
     public static Vector3 RetailSunVector(SkyKeyframe kf)
     {
@@ -325,9 +332,9 @@ public sealed class SkyStateProvider
         float sinP = MathF.Sin(p);
         float B = kf.DirBright;
         return new Vector3(
-            MathF.Sin(h) * B * cosP,    // x = sin(H) × B × cos(P)
-            cosP,                        // y = cos(P)        ← unscaled by B
-            B * sinP);                   // z = B × sin(P)
+            B * cosP * MathF.Sin(h),    // x = DirBright × cos(P) × sin(H)
+            B * cosP * MathF.Cos(h),    // y = DirBright × cos(P) × cos(H)
+            B * sinP);                   // z = DirBright × sin(P)
     }
 
     /// <summary>