Add Phase 3: object spawn system with catalogue UI

Spawn System:
- SpawnableComponent: marker component for Blueprint actors (name, category, thumbnail)
- SpawnCatalog DataAsset: lists all spawnable Blueprints with Factory for easy creation
- SpawnManager: loads catalog, spawns actors in front of camera, ensures Movable mobility
- Reads metadata from Blueprint component templates (no temp spawn needed)

Catalogue UI:
- Left panel with scrollable list grouped by category
- Thumbnail cards (80x80) with name below, click to spawn
- "Capture All Thumbnails" button on DataAsset: auto-generates from UE thumbnails

Undo/Redo improvements:
- SpawnAction: undo hides spawned actor, redo shows it
- Delete confirmation dialog (Yes/No) before soft-delete
- Undo/redo auto-deselects hidden actors and refreshes gizmo
- Proper cleanup of hidden actors when actions pruned from stack

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude/memory/reference_build.md

@@ -12,3 +12,7 @@ Build command (Editor target, Development):
 ```
 
 **How to apply:** Use this command to compile after code changes. Timeout should be set to 600000ms (10 min) for safety. The target name is `PS_ProserveEditorEditor` (Editor suffix) for editor builds.
+
+**When to use CLI vs Live Coding:**
+- Live Coding (Ctrl+Alt+F11): .cpp only changes (no new UCLASS, USTRUCT, UENUM, UPROPERTY in headers)
+- Full CLI build (UE must be closed): new files, header changes with new reflected types, Build.cs changes