wip(assembler): M3 round 4 -- plans built inside Unreal from the owner's strates; no import needed

SurfaceWorld and FloatingIslands plans generate at startup from the resolved seed,
strate types and heights (hashed, cached). Imported JSON is an opt-in override (off by
default); an invalid override shows an on-screen notice and falls back to legacy.
BuildHost on staged owner assets: SurfaceWorld cross-system checks, islands at owner
height (route, collision, anchors, BP edits), seed 137501, W1/W8/W16, Core-off legacy.
XY-column cache verified (hashes kept); island LOD0 p95 91 ms vs 133 ms sprint deadline.
Not exercised: season-seed path (no Season in staged settings), rendered notice pixels.

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

Source/VoxelForge/Public/VoxelSettings.h

@@ -383,6 +383,11 @@ public:
     UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "Voxel|Strates")
     FString WorldAssemblyManifestHash;
 
+    /** Use imported JSON above instead of planning from the resolved settings and layout. */
+    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Voxel|Strates|World Assembly",
+        meta = (DisplayName = "Use Imported World Assembly Override"))
+    bool bUseWorldAssemblyManifestOverride = false;
+
 #if WITH_EDITORONLY_DATA
     UPROPERTY(EditAnywhere, Category = "Voxel|Strates|World Assembly", meta = (FilePathFilter = "json"))
     FFilePath SourceWorldAssemblyManifestJson;