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/GigLineGameModeBase.h

@@ -6,11 +6,16 @@
 
 /**
  * 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.
+ *
+ * Sets the first-person character as the default pawn and spawns it at the start
+ * point, so the demo runs with no Blueprint wiring. Gameplay tuning that belongs to
+ * designers still lives in Blueprint subclasses on top of this.
  */
 UCLASS()
 class GIGLINE_API AGigLineGameModeBase : public AGameModeBase
 {
 	GENERATED_BODY()
+
+public:
+	AGigLineGameModeBase();
 };