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>

docs/language/assets/assets-font.md

@@ -0,0 +1,21 @@
+---
+id: assets-font
+name: Assets.font
+category: assets
+kind: namespace-method
+tokens: Assets.font
+sig: Assets.font(name: s) -> int
+tip: A font loaded through the preload queue, by name.
+order: 9
+ns: Assets
+member: font
+---
+
+The font handle for a <code>.ttf</code> / <code>.ttc</code> that <code>Assets.enqueue</code> loaded under <code>name</code>; 0 while it is not loaded yet. The queue sorts by extension: images become sprites (<code>Assets.get</code>), sounds go to the audio bank (<code>Audio.play(name:)</code>), fonts here.
+
+```ludic
+# doc-check: skip — illustrative
+Assets.enqueue(name: "menu", path: "assets/fonts/PixelOperator.ttf")
+…
+menu_font = Assets.font(name: "menu")
+```