npc: AGigLineNPCPerson prefab + stable-named screenshots

- New C++ AGigLineNPCPerson: reusable NPC/pedestrian prefab built on the MPFB
  human. ACharacter capsule half-height 83 cm (total 1.66 m, head top ~1.66 m
  so a 1.60 m camera doesn't clip), the character skeletal mesh on the built-in
  mesh as the visible body (feet on Z 0), AutoPossessAI for 0.5.0 pedestrians.
  Staged at Z 0 in the review scene; captured as review-npc-prefab.png.
- AGigLineShotActor now names screenshots by stable camera name (no list-index
  prefix): inserting or reordering cameras no longer renumbers files or orphans
  the old ones. Re-rendered all review/demo shots with stable names.
- ue_build_review_map.py: chmod the target .umap before save_map (git marks maps
  444 on checkout, silently making save_map return False and dropping stages).
- Screenshots/README.md, ROADMAP, TODO updated for the prefab + stable names.
- DemoMap.umap rebuilt by the render pipeline (north buildings + demo cameras).

Game/GigLine/Source/GigLine/GigLineShotActor.cpp

@@ -27,8 +27,12 @@ void AGigLineShotActor::Tick(float DeltaSeconds)
 		if (SettleCountdown <= 0.f)
 		{
 			bWaitingForSettle = false;
-			const FString FileName = FString::Printf(TEXT("review-%02d-%s"), CurrentShot,
-				CurrentShot < ShotNames.Num() ? *ShotNames[CurrentShot] : *FString::FromInt(CurrentShot));
+			// Use the stable custom name only (no list-index prefix): inserting or
+			// reordering cameras must not renumber files and orphan the old ones.
+			const FString Name = CurrentShot < ShotNames.Num()
+				? ShotNames[CurrentShot]
+				: FString::FromInt(CurrentShot);
+			const FString FileName = FString::Printf(TEXT("review-%s"), *Name);
 			// Resolution is the game window's; the runner passes -ResX/-ResY.
 			FScreenshotRequest::RequestScreenshot(FileName, false, false);
 			bWaitingForScreenshot = true;