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/file/_section.md

@@ -0,0 +1,7 @@
+---
+id: file
+title: File
+order: 44
+---
+
+Raw file access over the C stdio calls, for programs that read and write their own formats. <a href="file-open"><code>File.open</code></a> returns a handle (or <code>null</code>), <a href="file-read"><code>File.read</code></a> / <a href="file-write"><code>File.write</code></a> move bytes through a <code>bytes</code> buffer, <a href="file-seek"><code>File.seek</code></a> / <a href="file-tell"><code>File.tell</code></a> position the cursor, and <a href="file-close"><code>File.close</code></a> releases the handle. For text and structured data prefer the higher-level <code>Fs</code>, <code>Json</code> and <code>Prefs</code> APIs.

docs/language/file/file-close.md

@@ -0,0 +1,19 @@
+---
+id: file-close
+name: File.close
+category: file
+kind: namespace-method
+tokens: File.close
+sig: File.close(file: f)
+tip: Close a handle from File.open.
+order: 6
+ns: File
+member: close
+---
+
+Flushes and releases the handle. Every successful <code>File.open</code> pairs with one <code>File.close</code>.
+
+```ludic
+# doc-check: skip — illustrative
+File.close(file: f)
+```

docs/language/file/file-open.md

@@ -0,0 +1,20 @@
+---
+id: file-open
+name: File.open
+category: file
+kind: namespace-method
+tokens: File.open
+sig: File.open(path: p, mode: m) -> pointer
+tip: Open a file (fopen); null when it cannot be opened.
+order: 1
+ns: File
+member: open
+---
+
+Opens <code>path</code> with a C <code>fopen</code> mode string (<code>"rb"</code>, <code>"wb"</code>, <code>"ab"</code>). Returns the handle, or <code>null</code> when the file cannot be opened — always test for it.
+
+```ludic
+# doc-check: skip — illustrative
+let f = File.open(path: "save/best.txt", mode: "rb")
+if f == null { return }
+```

docs/language/file/file-read.md

@@ -0,0 +1,20 @@
+---
+id: file-read
+name: File.read
+category: file
+kind: namespace-method
+tokens: File.read
+sig: File.read(file: f, buffer: b, count: n) -> int
+tip: Read up to n bytes into a buffer; returns the bytes read.
+order: 2
+ns: File
+member: read
+---
+
+Reads at most <code>count</code> bytes from the handle into <code>buffer</code> (a <code>bytes</code> allocation) and returns how many arrived; fewer than asked means the end of the file.
+
+```ludic
+# doc-check: skip — illustrative
+let buf = bytes(size + 1)
+let got = File.read(file: f, buffer: buf, count: size)
+```

docs/language/file/file-seek.md

@@ -0,0 +1,21 @@
+---
+id: file-seek
+name: File.seek
+category: file
+kind: namespace-method
+tokens: File.seek
+sig: File.seek(file: f, offset: o, whence: w)
+tip: Move the file cursor (0 start, 1 current, 2 end).
+order: 4
+ns: File
+member: seek
+---
+
+Positions the cursor at <code>offset</code> bytes from <code>whence</code>: 0 the start, 1 the current position, 2 the end. Seeking to the end and reading <code>File.tell</code> measures a file.
+
+```ludic
+# doc-check: skip — illustrative
+File.seek(file: f, offset: 0, whence: 2)
+let size = File.tell(file: f)
+File.seek(file: f, offset: 0, whence: 0)
+```

docs/language/file/file-tell.md

@@ -0,0 +1,19 @@
+---
+id: file-tell
+name: File.tell
+category: file
+kind: namespace-method
+tokens: File.tell
+sig: File.tell(file: f) -> int
+tip: The cursor position in bytes.
+order: 5
+ns: File
+member: tell
+---
+
+Returns the current cursor position in bytes from the start of the file.
+
+```ludic
+# doc-check: skip — illustrative
+let size = File.tell(file: f)
+```

docs/language/file/file-write.md

@@ -0,0 +1,20 @@
+---
+id: file-write
+name: File.write
+category: file
+kind: namespace-method
+tokens: File.write
+sig: File.write(file: f, buffer: b, count: n) -> int
+tip: Write n bytes from a buffer; returns the bytes written.
+order: 3
+ns: File
+member: write
+---
+
+Writes <code>count</code> bytes of <code>buffer</code> (a string or a <code>bytes</code> allocation) to the handle and returns how many were written.
+
+```ludic
+# doc-check: skip — illustrative
+let line = "best_floor=3\n"
+File.write(file: f, buffer: line, count: len(line))
+```