feat: first-person player with Enhanced Input

AGigLineCharacter: 1.75 m capsule, 1.60 m eye camera, 4 m/s walk, mouse look
scaled in degrees per second (no double DeltaTime), jump. Loaded ahead of a
Blueprint so the demo is playable with no assets wired by hand.

Tools/ue_create_input_assets.py builds /Game/Input headlessly: five 1D actions
and an 11-mapping context. One action per direction instead of per-key modifiers,
because modifier objects do not survive the save path here: a mapping's modifier
array serialises None, and dimensioning a 2D move with per-key axis masks would
need exactly those modifiers. The cost is four action assets rather than two.

Also adds a fourth review camera at eye height and documents it; its approval is
pending.

Game/GigLine/Source/GigLine/GigLineCharacter.h

@@ -0,0 +1,86 @@
+// First-person player character for the 0.1.0 walkable Hollywood block.
+
+#pragma once
+
+#include "CoreMinimal.h"
+#include "GameFramework/Character.h"
+#include "InputActionValue.h"
+#include "GigLineCharacter.generated.h"
+
+class UCameraComponent;
+class UInputAction;
+class UInputMappingContext;
+
+
+/**
+ * Walking first-person character.
+ *
+ * Movement is C++ and network-agnostic in the shapes it uses (Enhanced Input ->
+ * AddMovementInput), so a Blueprint subclass can retune values without touching
+ * code. Defaults are human-scale: 1.75 m capsule, 1.6 m eye height, 4 m/s walk.
+ */
+UCLASS()
+class GIGLINE_API AGigLineCharacter : public ACharacter
+{
+	GENERATED_BODY()
+
+public:
+	AGigLineCharacter();
+
+	virtual void BeginPlay() override;
+	virtual void SetupPlayerInputComponent(class UInputComponent* PlayerInputComponent) override;
+
+protected:
+	/** Loads the Enhanced Input assets from /Game/Input; called from BeginPlay. */
+	void LoadInputAssets();
+
+	/** Moves along the control yaw by the given forward/strafe amounts. */
+	void ApplyMove(float Forward, float Strafe);
+
+	/** Handles input actions to movement; assigned in C++ so the project runs with no assets. */
+	/** Forward/back and strafe are separate 1D actions, summed into one move. */
+	void MoveForward(const FInputActionValue& Value);
+	void MoveStrafe(const FInputActionValue& Value);
+	void MoveBack(const FInputActionValue& Value);
+	void MoveLeft(const FInputActionValue& Value);
+	void Look(const FInputActionValue& Value);
+	void StartJump();
+	void StopJump();
+
+	/** Mapping context for the gamepad and keyboard. */
+	UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category = "Input")
+	TObjectPtr<UInputMappingContext> MappingContext;
+
+	UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category = "Input")
+	TObjectPtr<UInputAction> MoveAction;
+
+	UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category = "Input")
+	TObjectPtr<UInputAction> MoveBackAction;
+
+	UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category = "Input")
+	TObjectPtr<UInputAction> StrafeAction;
+
+	UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category = "Input")
+	TObjectPtr<UInputAction> StrafeLeftAction;
+
+	UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category = "Input")
+	TObjectPtr<UInputAction> LookAction;
+
+	UPROPERTY(EditDefaultsOnly, BlueprintReadOnly, Category = "Input")
+	TObjectPtr<UInputAction> JumpAction;
+
+	UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "Camera")
+	TObjectPtr<UCameraComponent> FirstPersonCamera;
+
+	/** Degrees per second per unit of mouse input; defaults to Unreal's usual 45. */
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Camera")
+	float LookSensitivity = 45.0f;
+
+	/** Invert the pitch axis, for players who prefer it. */
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Camera")
+	bool bInvertLookY = false;
+
+	/** Walk speed in metres per second; converted to Unreal units on first use. */
+	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Movement")
+	float WalkSpeedMetresPerSecond = 4.0f;
+};