docs(overhaul): correct S5 c1 review comments

Remove the deleted outdoor-fallback claim, describe the visible-cell union as diagnostics rather than a shared admission answer, and distinguish the landscape particle, resident-light, and future shadow consumers.

Correct ParticleSystem complexity prose: only the SortedSet indexes have logarithmic lifecycle edges; the view list uses binary-search insertion with linear shift and linear removal.

Focused verification: Core ParticleSystemTests 47/47; App visibility/terrain/frame/renderer 38/38; AP-116 settings/live-object 3/3; git diff --check clean. No behavior, tests, register, or architecture change.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/AcDream.Core/Vfx/ParticleSystem.cs

@@ -14,16 +14,17 @@ public sealed class ParticleSystem : IParticleSystem
     private readonly EmitterDescRegistry _registry;
     private readonly Random _rng;
     private readonly Dictionary<int, ParticleEmitter> _byHandle = new();
-    // Handles are monotonic, so sorted indexes preserve retail emitter-spawn
-    // order while making every lifecycle edge O(log E). The old List.Remove
-    // hard-stop path was O(E) and became visible when portal routes retained
-    // thousands of finite/fading emitters.
+    // Handles are monotonic, so the SortedSet indexes preserve retail
+    // emitter-spawn order while making their lifecycle edges O(log E). Their
+    // predecessor List.Remove hard-stop path was O(E) and became visible when
+    // portal routes retained thousands of finite/fading emitters.
     private readonly SortedSet<int> _allHandles = [];
     private readonly SortedSet<int> _simulationHandles = [];
     // ApplyRetailView is a per-frame production path. SortedSet's enumerator
-    // allocates its traversal stack, so retain this subset as a sorted list;
-    // lifecycle mutations pay the binary insertion/removal cost and the
-    // warmed view walk stays allocation-free in emitter-spawn order.
+    // allocates its traversal stack, so retain this subset as a sorted list.
+    // Insertion uses a binary search followed by a linear list shift; removal
+    // searches and compacts linearly. Lifecycle mutations pay those costs so
+    // the warmed view walk stays allocation-free in emitter-spawn order.
     private readonly List<int> _worldSimulationHandles = [];
     private readonly SortedSet<int>[] _renderableHandlesByPass =
         [[], [], []];