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/Vfx/PhysicsScriptRunner.cs

@@ -139,15 +139,7 @@ public sealed class PhysicsScriptRunner
                 _active.RemoveAt(i);
         }
 
-        _active.Add(new ActiveScript
-        {
-            Script        = script,
-            ScriptId      = scriptId,
-            EntityId      = entityId,
-            AnchorWorld   = anchorWorldPos,
-            StartTimeAbs  = _now,
-            NextHookIndex = 0,
-        });
+        AddActiveScript(script, scriptId, entityId, anchorWorldPos, delaySeconds: 0);
 
         if (DiagEnabled)
         {
@@ -159,6 +151,24 @@ public sealed class PhysicsScriptRunner
         return true;
     }
 
+    private void AddActiveScript(
+        DatPhysicsScript script,
+        uint scriptId,
+        uint entityId,
+        Vector3 anchorWorldPos,
+        float delaySeconds)
+    {
+        _active.Add(new ActiveScript
+        {
+            Script        = script,
+            ScriptId      = scriptId,
+            EntityId      = entityId,
+            AnchorWorld   = anchorWorldPos,
+            StartTimeAbs  = _now + Math.Max(0f, delaySeconds),
+            NextHookIndex = 0,
+        });
+    }
+
     /// <summary>
     /// Advance every active script by <paramref name="dtSeconds"/>.
     /// Fires each hook whose <see cref="PhysicsScriptData.StartTime"/>
@@ -233,18 +243,18 @@ public sealed class PhysicsScriptRunner
         if (hook is CallPESHook call)
         {
             // CallPESHook.PES = sub-script id; Pause = delay before the
-            // sub-script starts (retail's ScriptManager links it into
-            // the list with StartTime = now + Pause). For our flat-list
-            // design we just recurse Play() — the sub-script schedules
-            // its own hooks from its own time zero. If Pause > 0 we
-            // delay by baking it into the sub-script's StartTimeAbs.
-            Play(call.PES, a.EntityId, a.AnchorWorld);
-            if (call.Pause > 0f && _active.Count > 0)
+            // sub-script starts. Retail links it into the active script
+            // list with StartTime = now + Pause; our flat list preserves
+            // that timing without replacing the currently running script.
+            var subScript = ResolveScript(call.PES);
+            if (subScript is null || subScript.ScriptData.Count == 0)
             {
-                var sub = _active[^1];
-                sub.StartTimeAbs = _now + call.Pause;
-                _active[^1] = sub;
+                if (DiagEnabled)
+                    Console.WriteLine($"[pes] CallPES: script 0x{call.PES:X8} not found / empty");
+                return;
             }
+
+            AddActiveScript(subScript, call.PES, a.EntityId, a.AnchorWorld, call.Pause);
             return;
         }