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/ui/_section.md

@@ -0,0 +1,7 @@
+---
+id: ui
+title: Ui
+order: 43
+---
+
+The retained-mode menu API over a <code>ui</code> block. <a href="ui-build"><code>Ui.build</code></a> constructs every declared widget tree once (after fonts and skins are loaded); <a href="ui-open"><code>Ui.open</code></a> makes one menu active and <a href="ui-close"><code>Ui.close</code></a> deactivates it; the frame loop ticks navigation on its own, an activation fires the <code>UiClicked</code> event, and <a href="ui-clicked"><code>Ui.clicked</code></a> is the polled form; <a href="ui-set_text"><code>Ui.set_text</code></a> updates a label or button, and <a href="ui-render"><code>Ui.render</code></a> draws the active menu (call it from an <code>Overlay</code> handler so it paints over the world). Every <code>id: Name</code> in a <code>ui</code> block mints a <code>UI_Name</code> handle.

docs/language/ui/ui-build.md

@@ -0,0 +1,21 @@
+---
+id: ui-build
+name: Ui.build
+category: ui
+kind: namespace-method
+tokens: Ui.build
+sig: Ui.build()
+tip: Construct every declared ui block (loads skins, measures fonts).
+order: 1
+ns: Ui
+member: build
+---
+
+Builds the widget trees of every <code>ui</code> block. Call it once, after the fonts and images the blocks reference are loaded — a loading scene's last step is the usual place.
+
+```ludic
+# doc-check: skip — illustrative
+handler Boot phase Start {
+  Ui.build()
+}
+```

docs/language/ui/ui-clicked.md

@@ -0,0 +1,21 @@
+---
+id: ui-clicked
+name: Ui.clicked
+category: ui
+kind: namespace-method
+tokens: Ui.clicked
+sig: Ui.clicked(id: UI_Name) -> bool
+tip: Was this control activated this frame? (polled form of UiClicked)
+order: 5
+ns: Ui
+member: clicked
+---
+
+True on the frame a focused control with that id was activated (Enter, Space, or pad A). The event form is <code>@On(UiClicked) handler … { if id == UI_Name { … } }</code>; either can <code>become</code> another scene.
+
+```ludic
+# doc-check: skip — illustrative
+handler Menu phase Update {
+  if Ui.clicked(id: UI_Play) { become Play }
+}
+```

docs/language/ui/ui-close.md

@@ -0,0 +1,21 @@
+---
+id: ui-close
+name: Ui.close
+category: ui
+kind: namespace-method
+tokens: Ui.close
+sig: Ui.close()
+tip: Deactivate the menu: no menu is open.
+order: 3
+ns: Ui
+member: close
+---
+
+Closes whatever menu is active, so nothing is drawn by <code>Ui.render</code> and no click can fire. A play scene opens with it so a menu left over from the title never lingers.
+
+```ludic
+# doc-check: skip — illustrative
+scene Play {
+  on enter { Ui.close() }
+}
+```

docs/language/ui/ui-open.md

@@ -0,0 +1,21 @@
+---
+id: ui-open
+name: Ui.open
+category: ui
+kind: namespace-method
+tokens: Ui.open
+sig: Ui.open(id: UI_Name)
+tip: Make one menu active and focus its first button.
+order: 2
+ns: Ui
+member: open
+---
+
+Activates the menu whose root has that id and moves keyboard focus to its first focusable control. Only one menu is active at a time; opening another replaces it.
+
+```ludic
+# doc-check: skip — illustrative
+scene Title {
+  on enter { Ui.open(id: UI_TitleMenu) }
+}
+```

docs/language/ui/ui-render.md

@@ -0,0 +1,21 @@
+---
+id: ui-render
+name: Ui.render
+category: ui
+kind: namespace-method
+tokens: Ui.render
+sig: Ui.render()
+tip: Draw the active menu.
+order: 7
+ns: Ui
+member: render
+---
+
+Draws the active menu at its laid-out position. Call it from a handler in the <code>Overlay</code> phase so the menu is painted over the engine-drawn world; it draws nothing while no menu is open.
+
+```ludic
+# doc-check: skip — illustrative
+layer Menu {
+  handler Draw phase Overlay { Ui.render() }
+}
+```

docs/language/ui/ui-set_text.md

@@ -0,0 +1,19 @@
+---
+id: ui-set_text
+name: Ui.set_text
+category: ui
+kind: namespace-method
+tokens: Ui.set_text
+sig: Ui.set_text(id: UI_Name, text: s)
+tip: Replace a label's or button's text.
+order: 6
+ns: Ui
+member: set_text
+---
+
+Sets the text of the label or button with that id; the menu re-lays itself out on its next tick. Interpolated strings make run stats one line.
+
+```ludic
+# doc-check: skip — illustrative
+Ui.set_text(id: UI_Stats, text: `floor {run.floor}  kills {run.kills}`)
+```

docs/language/ui/ui-tick.md

@@ -0,0 +1,21 @@
+---
+id: ui-tick
+name: Ui.tick
+category: ui
+kind: namespace-method
+tokens: Ui.tick
+sig: Ui.tick(key: k)
+tip: Advance navigation by one key (the frame loop does this for you).
+order: 4
+ns: Ui
+member: tick
+---
+
+Moves focus and activates controls from one key code. The frame loop calls it every frame with the frame key, so a game normally never calls it; it remains for programs that drive their own loop from <code>entry</code>.
+
+```ludic
+# doc-check: skip — illustrative
+entry {
+  Ui.tick(key: Input.key())
+}
+```