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/main.ludic

@@ -202,6 +202,7 @@ entry {
   else { g_windowed = has_target and has_systems() }
 
   g_parsing = false                               # lowering errors now locate by statement, not token
+  check_program()                                 # L4: the types agree before anything is emitted
   emit_program()
 
   # --emit-llvm, or no binary target: emit IR and stop (stdout when out is null).