Add rotation arc rings, scale cubes, and gizmo improvements

Rotation gizmo:
- Quarter-arc rings via UProceduralMeshComponent (3D solid with depth)
- Dynamic arc facing: arcs flip to face camera based on octant
- Grey guide lines from center to arc endpoints
- Screen-space rotation direction (correct from any camera angle)

Scale gizmo:
- Arrow shafts + cube tips for per-axis scale
- Center cube (grey) for uniform XYZ scale
- Local space orientation (gizmo aligns with actor rotation)

Other:
- Runtime confirmation dialog (replaces FMessageDialog)
- ProceduralMeshComponent plugin dependency added

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

.claude/memory/project_ps_editor.md

@@ -13,6 +13,7 @@ Key decisions:
 - Naming: PS_Editor_ prefix on all files/classes
 - Plugin path: Unreal/Plugins/PS_Editor/
 - AZERTY keyboard: arrows + A/Q for movement, E/R/T for modes
+- Selection outline: auto-generated post-process material (C++), 8-neighbor edge detection on CustomStencil
 
 ## Completed Phases
 
@@ -27,13 +28,15 @@ Key decisions:
 - Snap to ground (End), soft-delete (Delete + confirmation dialog)
 - Undo/Redo (Ctrl+Z/Y, 50 action stack)
 - Properties panel + toolbar UI
-- Material: M_PS_Editor_Gizmo (Unlit, "Color" param, Translucent, Disable Depth Test)
+- Materials: M_PS_Editor_Gizmo (Unlit, "Color" param, Translucent, Disable Depth Test)
+- Selection outline: auto-generated PP material, BL_SceneColorAfterDOF, Lerp blend, color AF1500, 1px
+- Outline material auto-created via OnPostEngineInit, uses InvSize for resolution-independent offsets
 
 ### Phase 3 - Object Spawning
 - SpawnableComponent: marker on BPs (name, category, thumbnail)
 - SpawnCatalog DataAsset + Factory for easy creation
 - SpawnManager: spawns in front of camera, tracks all spawned actors
-- Catalogue UI: thumbnail cards, click to spawn, grouped by category
+- Catalogue UI: thumbnail cards (80x80), click to spawn, grouped by category
 - CaptureAllThumbnails on DataAsset: auto-generates from UE thumbnails
 - Spawn undo/redo, auto-deselect hidden actors
 
@@ -44,4 +47,4 @@ Key decisions:
 - UI: Save field + button, New Scene, saved scenes list with click-to-load
 
 ## Next: Phase 5 - Advanced Editing
-- Splines, lighting, AI characters, property editing
+- Splines, lighting, AI characters, property editing, duplication (Ctrl+D)