Add typed DamageEvent contract for the unified hit pipeline

The single payload every attack will route through, replacing the stringly
Object.call(&"take_sword_hit", "gored") paths. Standalone for now; the
per-actor slices wire hitbox.gd and the bull/matador/bear receivers onto it.

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

damage_event.gd

@@ -0,0 +1,43 @@
+class_name DamageEvent
+extends RefCounted
+## The one typed payload for every hit in the game — a bull goring a matador, a bear slam popping
+## the bull, a thrown spear landing. It replaces the scattered, stringly Object.call(&"take_sword_hit",
+## "gored") paths: an emitter (a Hitbox) fills one of these and hands it to the target's
+## receive_damage(event). One shape to read, log and type-check, instead of four call conventions.
+##
+## It serves both victim models the game already has: the bull, which dies on one clean hit
+## (lethal + cause + hit_position), and an enemy, which is launched/ragdolled by an impulse
+## (knockback_dir · knockback_strength + knock_up). A given hit just leaves the fields it doesn't
+## use at their defaults.
+
+enum Cause { GENERIC, GORED, MAULED, THROWN, SLAMMED, KICKED, DASHED }
+
+## Who dealt the hit — for attribution and for ignoring self-overlap. May be null.
+var source: Node = null
+## What kind of hit; drives the victim's reaction (blood/vignette/FX) and any future resistances.
+var cause: Cause = Cause.GENERIC
+## World contact point, so impact FX spawn where the hit actually landed.
+var hit_position: Vector3 = Vector3.ZERO
+## Planar push direction (need not be normalised). Vector3.ZERO = no horizontal knockback.
+var knockback_dir: Vector3 = Vector3.ZERO
+## Impulse magnitude behind knockback_dir — the enemy launch/ragdoll strength.
+var knockback_strength: float = 0.0
+## Upward launch in m/s (an overhead smash pop, a leap-slam outer ring). 0 = a grounded hit.
+var knock_up: float = 0.0
+## One clean hit ends the run for the bull; most enemy-dealt hits are lethal to it. Enemies that
+## are merely launched (not killed) by the bull's abilities set this false.
+var lethal: bool = true
+
+
+static func make(kind: Cause, at: Vector3, src: Node = null) -> DamageEvent:
+	var e := DamageEvent.new()
+	e.cause = kind
+	e.hit_position = at
+	e.source = src
+	return e
+
+
+## Lower-case name of the cause, for logs and for the bull's existing cause-keyed reactions
+## ("gored" / "mauled" / "thrown") during the migration off string causes.
+func cause_name() -> String:
+	return String(Cause.keys()[cause]).to_lower()