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.

Tools/ue_build_review_map.py

@@ -100,6 +100,9 @@ try:
             unreal.Vector(900, -1100, 500),
             unreal.Vector(200, -300, 160),
             unreal.Vector(200, 100, 200),
+            # first-person eye height, just south-east of the character: this is the
+            # view a player has at spawn, capsule and camera stack in frame
+            unreal.Vector(120, -260, 165),
         ])
         shots.set_editor_property("shot_rotations", [
             unreal.MathLibrary.find_look_at_rotation(
@@ -108,10 +111,13 @@ try:
                 unreal.Vector(200, -300, 160), unreal.Vector(0, 0, 85)),
             unreal.MathLibrary.find_look_at_rotation(
                 unreal.Vector(200, 100, 200), unreal.Vector(0, 600, 50)),
+            unreal.MathLibrary.find_look_at_rotation(
+                unreal.Vector(120, -260, 165), unreal.Vector(-200, 600, 90)),
         ])
-        shots.set_editor_property("shot_names", ["overview", "character", "scale-cubes"])
+        shots.set_editor_property("shot_names",
+                                  ["overview", "character", "scale-cubes", "first-person"])
         shots.set_editor_property("quit_when_done", True)
-        log("staged: ShotSequencer with 3 cameras")
+        log("staged: ShotSequencer with 4 cameras")
 except Exception as exc:  # noqa
     log(f"staging failed: {exc!r}")