feat(light): render-quality tiers 3-4 — cones, falloff, soft shadows, gels, normals, day/night (#49)

The remaining lighting tiers from the original proposal, all extending the
deterministic accumulation core (light.ludic) — no new ECS plumbing:

- Light.spot: cone / flashlight lights (direction + spread degrees), with a
  self-contained integer atan2-in-degrees and a feathered edge.
- Light.falloff: a brightness-ramp exponent (1 linear, 2 quadratic, …) via
  repeated fixed multiply.
- Light.soft: soft shadows — an area-sampled light so an occluder edge fades
  through a penumbra instead of a hard cut.
- Light.gel + Light.clear_gel: colour cookies — a light gels from its centre
  colour to a rim colour.
- Light.normal + Light.clear_normals + Light.height: a normal G-buffer so
  surfaces shade by facing (N·L), not distance alone (tier 3).
- Light.time_of_day: a day/night ambient ramp from a single 0..1 value.

The engine lighting system (systems_light.ludic) consumes matching optional
Light2D fields — direction/spread/falloff/softness/gel — each defaulting off so
an older five-field Light2D lights exactly as before. Every tier is integer +
Q16.16 fixed, so scenes light identically on every run and headless.

Worked example + regression: examples/library/light_tiers.ludic (1 1 1 1 1 1 1 1 1).
Nine new docs/language/light pages. Full suite 76 passed, self-host C-free
fixpoint intact, no golden drift.

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

selfhost/backend/emit_call.ludic

@@ -273,8 +273,17 @@ function emit_ns_call(ns: pointer, meth: pointer, e: Node) -> Val {
   if (ns == "Light") {
     if (meth == "ambient")         { bare = "light_ambient";         push(labels, "color") }
     if (meth == "point")           { bare = "light_point";           push(labels, "x"); push(labels, "y"); push(labels, "radius"); push(labels, "color"); push(labels, "energy") }
+    if (meth == "spot")            { bare = "light_spot";            push(labels, "x"); push(labels, "y"); push(labels, "radius"); push(labels, "color"); push(labels, "energy"); push(labels, "direction"); push(labels, "spread") }
     if (meth == "occlude")         { bare = "light_occlude";         push(labels, "x"); push(labels, "y"); push(labels, "width"); push(labels, "height") }
     if (meth == "clear_occluders") { bare = "light_clear_occluders" }
+    if (meth == "falloff")         { bare = "light_set_falloff";     push(labels, "exponent") }
+    if (meth == "soft")            { bare = "light_set_soft";        push(labels, "radius") }
+    if (meth == "gel")             { bare = "light_set_gel";         push(labels, "color") }
+    if (meth == "clear_gel")       { bare = "light_clear_gel" }
+    if (meth == "height")          { bare = "light_set_height";      push(labels, "height") }
+    if (meth == "normal")          { bare = "light_normal_rect";     push(labels, "x"); push(labels, "y"); push(labels, "width"); push(labels, "height"); push(labels, "nx"); push(labels, "ny") }
+    if (meth == "clear_normals")   { bare = "light_clear_normals" }
+    if (meth == "time_of_day")     { bare = "light_time_of_day";     push(labels, "t") }
   }
   # Query.* — ECS spatial queries over the reflection ABI (runtime/native/query.ludic,
   # spliced on demand). `prop` is a property id (World.prop_id); the spatial forms