feat(lang): 0.R1 - actions and reducers

action Name { fields } is a typed record; reducer State on Action(s: mut State, a: Action) { ... }
in the module that owns the state takes exactly that state and the action (a second state is
refused); dispatch Action { fields } queues one from anywhere, the queue supplied by the runtime.
The queue is drained at the end of every phase of the frame loop, after every phase of ludic.base's
core_tick_all, and by drain_actions(): in dispatch order, each action's reducers in the order of
their states' names, an action a reducer dispatches queued behind, a queue still growing after 64
rounds stopped with the action named. Examples actions/pack, phases, runaway; rejects for a second
state, a reducer on a non-action and an unknown dispatch; ludic.base's actions_test; LANGUAGE.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

selfhost/backend/game/emit_game.ludic

@@ -345,6 +345,7 @@ function emit_calls_for_phase(phase: pointer) -> void {
   emit_engine_systems_for_phase(phase)               # engine-owned systems run after every user handler
   emit_dyn_systems_for_phase(phase)                  # #64: mod-registered systems run last
   if (phase == "Overlay") { emit_scene_menu_render() }   # a scene's `shows` menu paints last
+  if len(g_act_names) > 0 { emit(`  call void {fn_sym("drain_actions")}()\n`) }   # 0.R: this phase's actions, reduced
 }
 
 # the menu of the live `scene X shows Menu`, drawn on top of everything else