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/PS_ProserveEditor.uproject

@@ -17,6 +17,10 @@
 			"TargetAllowList": [
 				"Editor"
 			]
+		},
+		{
+			"Name": "PS_Editor",
+			"Enabled": true
 		}
 	]
 }