Route the bull's hits through the typed DamageEvent pipeline

Hitbox now builds a DamageEvent (cause + hit position + shaped knock-up) and
calls the bull's new receive_damage(), instead of two stringly Object.call()s.
receive_damage adapts over the existing pip/knock-up logic so behaviour is
identical -- the characterization test drives both the string and typed paths
and asserts the same outcomes. Wire fx/damage/harness tests into run_tests.sh
+ CLAUDE.md. All hitbox guard tests green (stab, bear hitbox, ram, charge).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CmG3mQGVXZUPDVapmdbWZ1

hitbox.gd

@@ -80,11 +80,17 @@ func _apply_hit(body: Node3D) -> void:
 		return
 	_hit_this_swing[body] = true
 	_did_hit = true
-	body.call(&"take_sword_hit", damage_cause)
-	if knock_up > 0.0:
-		var v := _knock_up_for(body)
-		if v > 0.0:
-			body.call(&"apply_knock_up", v)
+	if body.has_method(&"receive_damage"):
+		var event := DamageEvent.make(DamageEvent.cause_from(damage_cause), body.global_position, self)
+		if knock_up > 0.0:
+			event.knock_up = _knock_up_for(body)
+		body.call(&"receive_damage", event)
+	else:
+		body.call(&"take_sword_hit", damage_cause)
+		if knock_up > 0.0:
+			var v := _knock_up_for(body)
+			if v > 0.0:
+				body.call(&"apply_knock_up", v)
 
 
 # Scale the pop by how far the body is from this hitbox's origin (planar). See the export docs.