docs: add the memory convention and seed MEMORY.md

AGENTS.md now states that planned work is checkbox items in ROADMAP.md marked
open, in progress, or done, and that discoveries, gotchas, notes, and bugs go to
MEMORY.md for coordination between collaborators. MEMORY.md is seeded with what
this build-up actually cost: the Unreal read-only-home crash, Blender/Blosm
headless workarounds and the spherical projection, the tiled-TIFF DEM trap, the
reference licensing and throttling rules, and the LFS silent-blob trap.

Also stages the concurrently created Unreal project files, and stops per-project
Build/ output (FileOpenOrder logs) from entering the repository.

Game/GigLine/Source/GigLine/GigLineGameModeBase.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include "CoreMinimal.h"
+#include "GameFramework/GameModeBase.h"
+#include "GigLineGameModeBase.generated.h"
+
+/**
+ * Default game mode for the 0.1.0 walkable Hollywood block demo.
+ * First-person movement is Blueprint-driven on top of Enhanced Input;
+ * this class exists so the project has a valid primary game module.
+ */
+UCLASS()
+class GIGLINE_API AGigLineGameModeBase : public AGameModeBase
+{
+	GENERATED_BODY()
+};