Lifecycle hooks: @OnStart/@OnQuit, @OnDespawn, @OnAttach (like @OnSpawn)

Adds the rest of the game/entity/property lifecycle as @-hooks, each firing at
one timeline moment and reducing to ordinary code:

- @OnStart / @OnQuit (program): @OnStart aliases the Start phase; @OnQuit runs in
  the frame loop's done: block, after the loop stops and before teardown.
- @OnDespawn(Model) (entity): a destructor. Despawn doesn't statically know the
  entity's model, so hooks compile to @on_despawn_<Model>(entity) functions and
  emit_despawn dispatches on @L_kind. Symmetric with @OnSpawn.
- @OnAttach(Property): fires in emit_init_component once a property is attached
  and seeded, with the property bound by name.

Registries + parsing mirror @OnSpawn. examples/lifecycle.ludic narrates the whole
timeline (output 1 700 50 950 2). Behaviour-preserving (goldens byte-identical,
despawn users unaffected when no hooks registered); test.sh 16/16, fixpoint holds.

Deferred: @OnDetach (per-property runtime dispatch) and scene @OnEnter/@OnExit
(need scene support in the compiler).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/emit_spawn.ludic

@@ -37,6 +37,16 @@ fn emit_init_component(e: ptr, comp: ptr, rec: Node) -> void {
       j = j + 1
     }
   }
+  # @OnAttach(Property) runs once the property is attached and seeded
+  let ab = onattach_body(comp)
+  if not ptr_is_null(ab) {
+    let save = nloc
+    let vslot = emit_alloca("ptr")
+    emit("  store ptr ");  emit(slot);  emit(", ptr ");  emit(vslot);  emit("\n")
+    loc_push(comp, vslot, comp)
+    emit_block(ab)
+    nloc = save
+  }
 }
 
 # bind each of a model's properties to entity `e`'s component storage, so an
@@ -87,5 +97,21 @@ fn emit_spawn(st: Node) -> void {
 
 fn emit_despawn(st: Node) -> void {
   let v = emit_expr(st.a)
+  # @OnDespawn: dispatch on the entity's kind and run the matching model's hook
+  if len(g_ondespawn) > 0 {
+    let me = itoa(MAX_ENT)
+    let kp = nreg();  emit("  ");  emit(kp);  emit(" = getelementptr inbounds [");  emit(me);  emit(" x i32], ptr @L_kind, i32 0, i32 ");  emit(v.code);  emit("\n")
+    let kind = emit_bind(sconcat("load i32, ptr ", kp))
+    let i = 0
+    while i < len(g_ondespawn) {
+      let mname = g_ondespawn[i].s
+      let c = emit_bind(sconcat("icmp eq i32 ", sconcat(kind, sconcat(", ", itoa(find_arch_id(mname))))))
+      let yes = lbl("dh");  let no = lbl("dhn")
+      emit("  br i1 ");  emit(c);  emit(", label %");  emit(yes);  emit(", label %");  emit(no);  emit("\n")
+      emit(yes);  emit(":\n  call void @on_despawn_");  emit(mname);  emit("(i32 ");  emit(v.code);  emit(")\n")
+      emit("  br label %");  emit(no);  emit("\n");  emit(no);  emit(":\n")
+      i = i + 1
+    }
+  }
   emit("  call void @L_free_entity(i32 ");  emit(v.code);  emit(")\n")
 }