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>

examples/library/input_movement.ludic

@@ -0,0 +1,25 @@
+# input_movement.ludic — Input.axis_i (#79): turn WASD into a -1/0/1 movement
+# intent as a plain int, with no bool->int glue (`ki(key_down('d')) - ...`). It
+# reads the multi-key device set and feeds an int mover directly. Driven headless
+# by injection, the same way the #50 device tests are.
+#
+# Deterministic; a full run prints:  1 0 -1 -1 0
+program InputMovement {
+  entry {
+    Input.press('d')                 # hold right
+    Input.poll()
+    print(Input.axis_i('a', 'd'))    # 1  — dx = right
+    print(Input.axis_i('w', 's'))    # 0  — dy = none
+
+    Input.release('d')
+    Input.press('a')                 # hold left
+    Input.press('w')                 # and up
+    Input.poll()
+    print(Input.axis_i('a', 'd'))    # -1 — dx = left
+    print(Input.axis_i('w', 's'))    # -1 — dy = up
+
+    Input.press('d')                 # now both left AND right held
+    Input.poll()
+    print(Input.axis_i('a', 'd'))    # 0  — opposing keys cancel
+  }
+}