feat(vfx): Phase C.1 — PES particle renderer + post-review fixes

Ports retail's ParticleEmitterInfo / Particle::Init / Particle::Update
(0x005170d0..0x0051d400) and PhysicsScript runtime to a C# data-layer
plus a Silk.NET billboard renderer. Sky-PES path is debug-only behind
ACDREAM_ENABLE_SKY_PES because named-retail decomp confirms GameSky
copies SkyObject.pes_id but never reads it (CreateDeletePhysicsObjects
0x005073c0, MakeObject 0x00506ee0, UseTime 0x005075b0).

Post-review fixes folded into this commit:

H1: AttachLocal (is_parent_local=1) follows live parent each frame.
    ParticleSystem.UpdateEmitterAnchor + ParticleHookSink.UpdateEntityAnchor
    let the owning subsystem refresh AnchorPos every tick — matches
    ParticleEmitter::UpdateParticles 0x0051d2d4 which re-reads the live
    parent frame when is_parent_local != 0. Drops the renderer-side
    cameraOffset hack that only worked when the parent was the camera.

H3: Strip the long stale comment in GfxObjMesh.cs that contradicted the
    retail-faithful (1 - translucency) opacity formula. The code was
    right; the comment was a leftover from an earlier hypothesis and
    would have invited a wrong "fix".

M1: SkyRenderer tracks textures whose wrap mode it set to ClampToEdge
    and restores them to Repeat at end-of-pass, so non-sky renderers
    that share the GL handle can't silently inherit clamped wrap state.

M2: Post-scene Z-offset (-120m) only fires when the SkyObject is
    weather-flagged AND bit 0x08 is clear, matching retail
    GameSky::UpdatePosition 0x00506dd0. The old code applied it to
    every post-scene object — a no-op today (every Dereth post-scene
    entry happens to be weather-flagged) but a future post-scene-only
    sun rim would have been pushed below the camera.

M4: ParticleSystem.EmitterDied event lets ParticleHookSink prune dead
    handles from the per-entity tracking dictionaries, fixing a slow
    leak where naturally-expired emitters' handles stayed in the
    ConcurrentBag forever during long sessions.

M5: SkyPesEntityId moves the post-scene flag bit to 0x08000000 so it
    can't ever overlap the object-index range. Synthetic IDs stay in
    the reserved 0xFxxxxxxx space.

New tests (ParticleSystemTests + ParticleHookSinkTests):
- UpdateEmitterAnchor_AttachLocal_ParticlePositionFollowsLiveAnchor
- UpdateEmitterAnchor_AttachLocalCleared_ParticleFrozenAtSpawnOrigin
- EmitterDied_FiresOncePerHandle_AfterAllParticlesExpire
- Birthrate_PerSec_EmitsOnePerTickWhenIntervalElapsed (retail-faithful
  single-emit-per-frame behavior)
- UpdateEntityAnchor_WithAttachLocal_MovesParticleToLiveAnchor
- EmitterDied_PrunesPerEntityHandleTracking

dotnet build green, dotnet test green: 695 / 393 / 243 = 1331 passed
(up from 1325).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Meshing/GfxObjSubMesh.cs

@@ -13,67 +13,40 @@ public sealed record GfxObjSubMesh(
 {
     /// <summary>
     /// How this sub-mesh should be composited into the frame.
-    /// Populated from Surface.Type flags at upload time (requires a DatCollection).
-    /// Defaults to <see cref="TranslucencyKind.Opaque"/> so offline fixtures
-    /// that don't supply dat access compile and pass unchanged.
+    /// Populated from Surface.Type flags at upload time.
     /// </summary>
     public TranslucencyKind Translucency { get; init; } = TranslucencyKind.Opaque;
 
     /// <summary>
-    /// Self-illumination strength of the Surface (<c>Surface.Luminosity</c>
-    /// field, 0..1 fraction — NOT the <c>SurfaceType.Luminous</c> flag bit).
-    /// Retail uses this as an emissive coefficient in the per-vertex
-    /// lighting formula:
-    /// <code>
-    ///   tint = clamp(vec3(Luminosity) + AmbColor + diffuse * DirColor, 0, 1)
-    ///   fragment = texture * tint
-    /// </code>
-    /// For Dereth's sky meshes, the DOME (0x010015EE) and SUN/MOON
-    /// (0x01001348) have <c>Luminosity=1.0</c> (self-illuminated — emissive
-    /// saturates the lighting math so the baked texture always renders
-    /// at full brightness). CLOUDS (0x010015EF, 0x01004C36) have
-    /// <c>Luminosity=0.0</c> (lit by ambient+diffuse — pick up the
-    /// time-of-day tint). See
-    /// <c>docs/research/2026-04-23-sky-retail-verbatim.md</c> §6.
-    /// Defaults to 0.0 (fully lit) so non-sky meshes render through the
-    /// normal lighting path without change.
+    /// Surface.Luminosity. Retail uses this as material emissive.
     /// </summary>
     public float Luminosity { get; init; } = 0f;
 
     /// <summary>
-    /// True when at least one vertex's UV component lies outside the
-    /// <c>[0, 1]</c> range, meaning the mesh was authored to have its
-    /// texture tile across the geometry (i.e. it expects
-    /// <c>GL_REPEAT</c>/<c>D3DTADDRESS_WRAP</c>). The sky renderer reads
-    /// this to decide between <c>GL_REPEAT</c> (this flag set, or any
-    /// scrolling layer) and <c>GL_CLAMP_TO_EDGE</c> (all UVs strictly
-    /// in <c>[0,1]</c>), which avoids wall-seam bleed on the dome
-    /// (UVs in <c>[0,1]</c>) while still tiling the inner star/cloud
-    /// layers (UVs in <c>[~0.4, ~4.6]</c>) correctly.
-    /// Defaults to false so non-sky consumers get the previous behavior.
+    /// Surface.Diffuse. Retail sky keyframes route SkyObjectReplace.MaxBright
+    /// through CPhysicsObj::SetDiffusion (0x005119e0), which lands in
+    /// CMaterial::SetDiffuseSimple (0x00539750).
+    /// </summary>
+    public float Diffuse { get; init; } = 1f;
+
+    /// <summary>
+    /// True when at least one vertex UV component lies outside [0, 1], so
+    /// the mesh expects texture repeat instead of clamp.
     /// </summary>
     public bool NeedsUvRepeat { get; init; } = false;
 
     /// <summary>
-    /// <c>Surface.Translucency</c> float (0..1) treated as an OPACITY
-    /// multiplier on fragment alpha. 1.0 = fully opaque (default for
-    /// non-Translucent surfaces). Distinct from the
-    /// <see cref="TranslucencyKind"/> classifier above, which buckets the
-    /// flag bits. Retail's <c>D3DPolyRender::SetSurface</c> at
-    /// <c>0x59c7a6</c> (decomp lines 425255-425260) reads
-    /// <c>Surface.Translucency</c> when the <c>Translucent</c> (0x10) bit
-    /// is set, computes <c>curr_alpha = _ftol2(translucency × 255)</c>,
-    /// and writes that as vertex alpha — i.e. the dat's Translucency float
-    /// is used DIRECTLY as opacity, NOT inverted. ACViewer
-    /// (<c>TextureCache.cs:142</c>) and WorldBuilder
-    /// (<c>ObjectMeshManager.cs:1115</c>) both use <c>1 - translucency</c>
-    /// and are wrong by the same misread.
-    /// For the rain Surface 0x080000C5 (translucency=0.5): opacity = 0.5;
-    /// with the <c>(SrcAlpha, One)</c> additive blend the rain streaks
-    /// contribute at half intensity. For cloud surface 0x08000023
-    /// (translucency=0.25): opacity = 0.25 (matches retail's dim clouds).
-    /// Defaults to 1.0 (fully opaque) so non-Translucent surfaces render
-    /// at full opacity without change.
+    /// Final opacity multiplier derived from Surface.Translucency. Retail
+    /// translucency is transparency: 0.0 is opaque and 1.0 is invisible.
+    /// CMaterial::SetTranslucencySimple at 0x005396f0 writes material alpha
+    /// as 1 - translucency.
     /// </summary>
-    public float SurfTranslucency { get; init; } = 1f;
+    public float SurfOpacity { get; init; } = 1f;
+
+    /// <summary>
+    /// True when the raw Surface.Type has the Additive bit. Retail disables
+    /// fixed-function fog alpha for this raw bit even if the final blend mode
+    /// is forced to AlphaBlend by the Translucent+ClipMap branch.
+    /// </summary>
+    public bool DisableFog { get; init; } = false;
 }