qa: make the demo walkable — terrain collision root cause, spawn, scripted QA

The reported fall-through was a misdiagnosis: the player never fell. The
imported Terrain_DEM had only a bounding-box simple collision proxy, so a
downward trace anywhere in the block hit the terrain at Z 819 (the mesh
bbox max) and the street sat under an invisible 8 m lid. Standing on that
box looked plausible, which is why it read as working.

- add UGigLineAssetTools (C++): force CTF_UseComplexAsSimple on a static
  mesh. UE 5.8 dropped bUseComplexAsSimpleCollision and Python cannot set
  the flag; the builder also saves the asset, since the flag lives there
  and a map-only save silently reverts it.
- spawn (-13336, -1150, 600): inside the carved corridor (the cut is a
  10.7 m half-width around the road centreline), lands on the road at 456.
- fix ResetToStart returning to the mid-air PlayerStart captured in
  BeginPlay: StartLocation is now captured on the first grounded frame.
- HighResShot 1280x720 instead of "1280 720", which is a multiplier.
- add -qaselftest: scripted walk/reset/pause on a core ticker plus a
  swept ground transect. Results: walk 746 cm/2 s with Z steady, reset
  0 cm from spawn, pause/unpause 1/0, transect 84 samples 0 holes.
- rebase onto main, keeping the frontage materials and placement fixes.

Game/GigLine/Source/GigLine/GigLineGameModeBase.cpp

@@ -1,5 +1,6 @@
 #include "GigLineGameModeBase.h"
 
+#include "GameFramework/PlayerController.h"
 #include "GigLineCharacter.h"
 #include "GigLineHUD.h"
 
@@ -9,3 +10,12 @@ AGigLineGameModeBase::AGigLineGameModeBase()
 	// ODbL attribution must be visible in the running demo, not only in docs.
 	HUDClass = AGigLineHUD::StaticClass();
 }
+
+void AGigLineGameModeBase::HandleStartingNewPlayer_Implementation(APlayerController* NewPlayer)
+{
+	Super::HandleStartingNewPlayer_Implementation(NewPlayer);
+	UE_LOG(LogTemp, Log, TEXT("GigLine GM: player %s connected; pawn=%s input=%s"),
+		NewPlayer ? *NewPlayer->GetName() : TEXT("null"),
+		NewPlayer && NewPlayer->GetPawn() ? *NewPlayer->GetPawn()->GetName() : TEXT("NONE"),
+		NewPlayer && NewPlayer->PlayerInput ? TEXT("yes") : TEXT("no"));
+}