feat(ecs): Light2D/Occluder/Ambient as auto-consumed components (#47)

The ECS-native shape the 2D lighting follow-up asked for, built on the
engine-owned-system hook from #43. A torch is just an entity carrying
Light2D, a wall an entity carrying Occluder, and one Ambient entity sets
the night tint — the engine runs the whole deterministic light pass at the
end of the Render phase (ambient modulate -> carve occluder shadows ->
accumulate additive radial lights) and presents. No Light.* calls wired.

- runtime/native/systems_light.ludic: esys_light2d, consuming the components
  through the by-name reflection ABI and reusing the #4 accumulation core
  (light_ambient / light_occlude / light_point). Reads position from a
  Position component when present, else the light's own x/y.
- Split from systems.ludic so a SpriteAnim/Motion-only game never links the
  light pass; spliced (with light.ludic) only when Light2D/Occluder declared.
- emit_main now boots rt_init like the auto-loop/test runner, so an
  entry-driven game that renders has its framebuffer allocated (headless:
  allocate only, no window, byte-identical stdout for non-rendering games).

Worked example + regression: examples/library/light_ecs.ludic (32 1 32 1).
Full suite 74 passed, self-host C-free fixpoint intact, no golden drift.

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

tools/x/test.ludic

@@ -246,6 +246,10 @@ function cmd_test() -> int {
   # game merely declares and carries — no handler wired. Entry-driven so it can
   # assert the auto-advanced fields at known tick counts.
   net_case("library/anim_ecs", "1 5 2 10 0 2 10 1 1")
+  # #47: the engine light pass consumes Light2D / Occluder / Ambient components at
+  # the end of the Render phase — ambient tint, additive glow, hard shadow — with
+  # no Light.* calls wired. Sampled back off the framebuffer with Screen.pixel.
+  net_case("library/light_ecs", "32 1 32 1")
 
   feat_case("events/recurse", "", "16", "recurse.ludic (EV6: re-entrant emit is depth-bounded, no runaway cycle)")
   net_case("events/scoped", "2")