fix: default map is the runnable DemoMap, not the engine template

A plain packaged launch (./GigLine.sh with no -map) opened
/Engine/Maps/Templates/OpenWorld — an empty engine template with nothing to
do, which presented as a 'stuck' window with no working mouse/keys. The
GameDefaultMap setting lived in DefaultGame.ini and wasn't taking effect.

Move GameMapsSettings (GameDefaultMap/EditorStartupMap/ServerDefaultMap/
TransitionMap = /Game/Hollywood/DemoMap) into DefaultEngine.ini alongside the
GlobalDefaultGameMode, and drop the stale ReviewMap default from DefaultGame.ini.
Verified: plain ./GigLine.sh now loads /Game/Hollywood/DemoMap, Enhanced Input
initializes, Vulkan window opens.

Game/GigLine/Config/DefaultEngine.ini

@@ -1,5 +1,11 @@
 [/Script/EngineSettings.GameMapsSettings]
 GlobalDefaultGameMode="/Script/GigLine.GigLineGameModeBase"
+; The runnable map is the walkable demo, so a plain launch opens it (not the
+; engine template nor the review staging scene).
+GameDefaultMap=/Game/Hollywood/DemoMap
+EditorStartupMap=/Game/Hollywood/DemoMap
+ServerDefaultMap=/Game/Hollywood/DemoMap
+TransitionMap=/Game/Hollywood/DemoMap
 
 [/Script/Engine.RendererSettings]
 ; Dynamic-only lighting. With static lighting allowed, the stationary sun and