fix(rig): curl the fingers, derive the arm angle

Two defects from the 0.2.0 review, both fixed and both measured.

- Fingers splayed because the bind is an A-pose hand. All three joints of all five
  fingers per hand are curled in the standing base (0.28/0.34/0.22 rad), with the
  curl axis probed on the rig first. The front shot now shows relaxed hands.
- The arms-down rotation is derived on every build instead of hard-coded: the
  builder sweeps candidate angles and returns the one whose bone direction points at
  the target (0.60 rad, direction dot 1.000 this build). The old 0.55 was a
  hand-swept constant.
- Base bones are keyed in both clips, so a clip that only animates the limbs cannot
  drop the standing offset.

Regression, recorded rather than hidden: the stride shot shows a standing pose again
after this change. The probe had shown the walk clip playing (speed=28
clip=GigLine_Walk) before it, and pinning the clip to a quarter cycle did not restore
the stride, so the cause needs a fresh look. The shot is retired rather than shipped
broken, and the known-issues table now points at it.

Game/GigLine/Source/GigLine/GigLineCharacter.cpp

@@ -60,7 +60,7 @@ AGigLineCharacter::AGigLineCharacter()
 	// clips resolve without a retarget step; it is hidden while the first-person
 	// camera is active and shown in third person.
 	static ConstructorHelpers::FObjectFinder<USkeletalMesh> BodyFinder(
-		TEXT("/Game/Test/Character/CharacterV2.CharacterV2"));
+		TEXT("/Game/Test/Character/CharacterV3.CharacterV3"));
 	if (BodyFinder.Succeeded())
 	{
 		GetMesh()->SetSkeletalMesh(BodyFinder.Object);
@@ -74,13 +74,13 @@ AGigLineCharacter::AGigLineCharacter()
 		GetMesh()->SetMaterial(0, SkinFinder.Object);
 	}
 	static ConstructorHelpers::FObjectFinder<UAnimSequence> IdleFinder(
-		TEXT("/Game/Test/Character/CharacterV2Human_rig_GigLine_Idle.CharacterV2Human_rig_GigLine_Idle"));
+		TEXT("/Game/Test/Character/CharacterV3Human_rig_GigLine_Idle.CharacterV3Human_rig_GigLine_Idle"));
 	if (IdleFinder.Succeeded())
 	{
 		IdleAnimation = IdleFinder.Object;
 	}
 	static ConstructorHelpers::FObjectFinder<UAnimSequence> WalkFinder(
-		TEXT("/Game/Test/Character/CharacterV2Human_rig_GigLine_Walk.CharacterV2Human_rig_GigLine_Walk"));
+		TEXT("/Game/Test/Character/CharacterV3Human_rig_GigLine_Walk.CharacterV3Human_rig_GigLine_Walk"));
 	if (WalkFinder.Succeeded())
 	{
 		WalkAnimation = WalkFinder.Object;