wip(assembler): M3 round 3 -- separated islands + Unreal island route (owner build 18:46)

Islands read as separate (91.89% open sky at mid-height), underside cavity closed,
rim teeth were capture shading. Island manifest import + BuildHost proof passed on the
pre-cache tree; M1 SurfaceWorld and M2 V1/V2 gates passed.

Known open: final XY-column cache compiled in the owner build but is unverified;
island LOD0 p95 ~155 ms misses the 133 ms sprint deadline (legacy ~43 ms); the island
manifest only fits the BuildHost fixture layout (owner's world: Core init fails,
empty world) -> round 4 builds plans inside Unreal.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Source/VoxelForge/Public/VoxelSettings.h

@@ -373,10 +373,10 @@ public:
 	UPROPERTY(EditAnywhere, BlueprintReadOnly, Category = "Voxel|Strates")
 	TSoftObjectPtr<UVoxelSeasonAsset> Season;
 
-    // Optional reviewed Core surface plan. The canonical JSON stays in this cooked settings asset;
-    // its Core FNV digest is included in GetCurrentSeasonContentHash when present.
-    // Plan de surface Core facultatif; le JSON canonique est cuit avec les reglages et son hash
-    // Core est inclus dans GetCurrentSeasonContentHash lorsqu'il est present.
+    // Optional reviewed Core SurfaceWorld and FloatingIslands plans. Canonical JSON stays in this
+    // cooked settings asset; its Core FNV digest enters the season hash only while Core is enabled.
+    // Plans Core SurfaceWorld et FloatingIslands facultatifs. Le JSON canonique est cuit ici ;
+    // son hash FNV Core entre dans le hash de saison uniquement lorsque Core est actif.
     UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "Voxel|Strates", meta = (MultiLine = true))
     FString WorldAssemblyManifestJson;