Add PS_Editor plugin Phase 1: GameMode + Camera navigation

Runtime editor plugin with UE viewport-style camera controls:
- ZQSD/Arrows movement (always active), E/A for up/down
- LMB: pan (horizontal move + yaw), RMB: free fly look
- Alt+LMB / MMB: orbit around focal point, scroll: zoom
- HUD with controls help, cursor auto-hide during camera ops

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

Unreal/Config/DefaultEngine.ini

@@ -1,7 +1,9 @@
 
 
 [/Script/EngineSettings.GameMapsSettings]
-GameDefaultMap=/Engine/Maps/Templates/OpenWorld
+GameDefaultMap=/Game/test.test
+EditorStartupMap=/Game/test.test
+GlobalDefaultGameMode=/Script/PS_Editor.PS_Editor_GameMode
 
 [/Script/Engine.RendererSettings]
 r.AllowStaticLighting=False