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>

examples/rejected/every_error.ludic

@@ -0,0 +1,11 @@
+# L4: every mix-up in a program is reported at once, not only the first
+program EveryError {
+  function half(n: int) -> int { return n / 2 }
+  function name() -> int { return "seven" }
+  entry {
+    let on = true
+    print(on + 1)
+    print(half(1, 2))
+    print(name())
+  }
+}