feat: third-person camera toggle (V) + fix first-person showing inside the model

The first-person head-shrink (SkeletonModifier3D) left the camera looking at
the inside of the neck/torso/hair. Replaced it: the owner's model now renders
shadows-only in first person (clean FPS view, still fully animated and visible
to others and in shadows).

Added a third-person toggle (V / toggle_camera_view) so you can actually see
your own animated model — the easiest way to verify a new skin's animations:
- over-the-shoulder SpringArm3D camera (wall-collision aware) on the local
  player; press V to swap, press again to return
- firing still uses the first-person camera, so aim is unchanged
- reveals the owner's model via set_owner_visible() on both SkinnedPlayerModel
  and HumanoidModel; hides the first-person weapon viewmodel while in TP
- death forces first person so the toggle can't fight the death cam

Smoke test extended to cover the toggle (camera boom created, becomes current,
round-trips) — 28/28 checks pass for both color and GLB skins.

Co-Authored-By: Claude Fable 5 <[email protected]>

characters/humanoid_model.gd

@@ -197,6 +197,19 @@ func _set_procedural_visible(on: bool) -> void:
 		if part:
 			part.visible = on
 
+## Show/hide the model to its OWNER (third-person toggle). off = shadows-only so
+## the local first-person camera doesn't see the body; on = fully visible.
+func set_owner_visible(on: bool) -> void:
+	var mode := GeometryInstance3D.SHADOW_CASTING_SETTING_ON if on \
+		else GeometryInstance3D.SHADOW_CASTING_SETTING_SHADOWS_ONLY
+	_set_owner_shadow_recursive(self, mode)
+
+func _set_owner_shadow_recursive(node: Node, mode: int) -> void:
+	if node is GeometryInstance3D:
+		node.cast_shadow = mode
+	for child in node.get_children():
+		_set_owner_shadow_recursive(child, mode)
+
 func _apply_color(col: Color) -> void:
 	var mat = StandardMaterial3D.new()
 	mat.albedo_color = col