feat(engine): #90 atlas-aware Sprite component, #91 become from listeners, 0.3.x ergonomics batch

Closes the two open issues and lands the pending unreleased batch:

- #90: `Sprite { atlas: 1 }` routes esys_sprite through atlas_draw_ex
  (scale/flip/tint), so cell / cell_span / strip ids of any size draw
  through the engine sprite-render system. examples/library/sprite_atlas
  is the pixel-readback regression.
- #91: `become` from an @On(Event) listener / global handler / plain
  function no longer segfaults the compiler; it emits @L_scene_leave()
  (a dispatch on the live scene id) so the leaving scene's on-exit runs.
  UI_* handles are readable from any code (widget table built on first
  use). examples/library/scene_menus covers it.
- fix: a windowed `ludicc -o` build that reaches the audio runtime only
  through the atlas/Assets preload import now links audio.ll +
  AVFoundation (the audio backend link was gated on a game-level
  Audio.* call, so any windowed game declaring Sprite failed to link).
- the hand-written "Unreleased" CHANGELOG section is converted to
  changesets under changes/ so `x release` generates it.
- plus the batch: engine-driven retained UI + UiClicked event, Overlay
  phase, TileSkin tilemap-render system, Key.* constants, Font/Ui/File
  namespaces, Sprite.strip, prefabs, managers, countdown fields,
  enum-typed machines, layer @Queries, ludic.prefs / ludic.dungeon
  packages, Ai.seek pathing, Solids.solid2, cursor confine (mode 3)
  fix, shooter centre-aim fix, reserved-word function diagnostic.

Verified: x test (124/124), x test-tools, check-impl, check-vocabulary,
check-docs, docs-gen + docs-check, bootstrap-cfree (seed is a fixpoint).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

runtime/native/ui_draw.ludic

@@ -164,6 +164,13 @@ function ui_focusables() -> int {
   return n
 }
 
+# a focused control was activated (Enter / Space / pad A): the event-driven form of
+# ui_clicked — `@On(UiClicked) handler { if id == UI_Play { ... } }`.
+event UiClicked { id: int = 0 }
+
+# Ui.close(): no menu is active (the same as opening root -1)
+function rt_ui_close() -> void { rt_ui_open(0 - 1) }
+
 function rt_ui_open(root: int) -> void {
   ui_active = root
   let n = ui_focusables()
@@ -172,8 +179,8 @@ function rt_ui_open(root: int) -> void {
 }
 
 function rt_ui_tick(k: int) -> void {
-  if ui_active < 0 { return }
-  for i in 0 .. ui_n { ui_fired[i] = 0 }
+  for i in 0 .. ui_n { ui_fired[i] = 0 }    # a closed UI clears clicks too, so a stale
+  if ui_active < 0 { return }               # activation never leaks to the next frame/scene
   ui_layout()
   let n = ui_focusables()
   if n == 0 {
@@ -196,9 +203,11 @@ function rt_ui_tick(k: int) -> void {
     cur = (cur + 1) % n
     ui_focus = ui_fl[cur]
   }
-  if k == 32 { ui_fired[ui_focus] = 1 }
-  if k == 10 { ui_fired[ui_focus] = 1 }
-  if k == 13 { ui_fired[ui_focus] = 1 }
+  var fire = 0
+  if k == 32 { fire = 1 }
+  if k == 10 { fire = 1 }
+  if k == 13 { fire = 1 }
+  if fire == 1 { ui_fired[ui_focus] = 1;  emit UiClicked(id: ui_focus) }
 }
 
 function rt_ui_render() -> void {