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/float_into_int.ludic

@@ -0,0 +1,10 @@
+# L4: a float computed into an int slot is refused - write int(x)
+program FloatIntoInt {
+  numbers float
+  entry {
+    let speed: float = 3.2
+    var metres: int = 0
+    metres = speed * 2.0
+    print(metres)
+  }
+}