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.cpp

@@ -1 +1,8 @@
 #include "GigLineGameModeBase.h"
+
+#include "GigLineCharacter.h"
+
+AGigLineGameModeBase::AGigLineGameModeBase()
+{
+	DefaultPawnClass = AGigLineCharacter::StaticClass();
+}