feat(lang): L4 type checker between parse and emit

selfhost/check/ walks every function, the entry, tests, globals' initializers and
@On listeners with real scopes, and refuses mixed number kinds, text and numbers,
two record types, mismatched slices and fn types, wrong argument counts, wrong
returns and wrong push elements - every mix-up at once, each at its line.
LUDIC_CHECK_REPORT=1 lists them by category. pointer stays untyped (L7's).

What it found is fixed: render3d's HDR scan calling the float-bits extern f_lt
with floats; ludic.shooter's right-stick aim overflowing past half a push;
prof.ludic storing longs in []int; extern arguments now coerced to their
parameters. Text-returning runtime functions say string; Assets.ready says bool.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

selfhost/backend/emit_fnval.ludic

@@ -79,7 +79,7 @@ function emit_indirect_call(fv: Val, e: Node) -> Val {
   }
   let rl = llty(ret)
   emit("  ")
-  var rreg = "0"
+  var rreg: pointer = "0"
   if not (rl == "void") {
     rreg = nreg()
     emit(rreg)