feat(input,ecs): #79 Input.axis_i directional int + #84 world bounds

#79 — Input.axis_i(neg,pos) -> int returns a -1/0/1 movement intent from the
multi-key device set, so WASD-to-movement needs no bool->int glue and feeds an
int mover directly (dx = Input.axis_i('a','d')).

#84 — a Bounds config entity (rect + policy, from ludic.core) drives the
engine-owned world-bounds system (LateUpdate): clamp / wrap / bounce (clamp +
flip Body velocity) / kill (despawn a body fully outside). Reads the Collider
size so the box stays inside; off by default, spliced only when Bounds is
declared (byte-identical otherwise). Adds World.despawn(e) — the by-id
reflective despawn (runs @OnDespawn + frees) via a new world_despawn intrinsic
whose @fn_world_despawn helper is emitted in emit_program's tail once a use is
seen (the g_uses_* prelude pattern), used by the kill policy and callable from
any system.

Examples input_movement + world_bounds. Full suite 112/0, goldens
byte-identical, fixpoint holds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/language/input/input-axis_i.md

@@ -0,0 +1,24 @@
+---
+id: input-axis_i
+name: Input.axis_i
+category: input
+kind: namespace-method
+tokens: Input.axis_i
+sig: Input.axis_i(neg, pos) -> int
+tip: A -1/0/1 directional intent as a plain int, no bool->int glue.
+order: 14
+ns: Input
+member: axis_i
+---
+
+Returns a directional intent as a plain <code>int</code>: <code>+1</code> when the positive key is held, <code>-1</code> when the negative one is, <code>0</code> for neither or both. It reads the multi-key device set, so it replaces the <code>ki(key_down('d')) - ki(key_down('a'))</code> boolean-to-int boilerplate and feeds an int mover directly — <code>dx = Input.axis_i('a', 'd')</code>, <code>dy = Input.axis_i('w', 's')</code>. For an analog / normalized value use <a href="input-axis.html"><code>Input.axis</code></a> (fixed) or <a href="input-vector.html"><code>Input.vector</code></a>.
+
+```ludic
+program Demo {
+  entry {
+    Input.press('d')
+    Input.poll()
+    print(Input.axis_i('a', 'd'))     # 1
+  }
+}
+```