Fix float arithmetic codegen and math_log aliasing

Float + previously fell through to string concat (segfault); -, *, /, %
operated on raw IEEE-754 bit patterns as integers (garbage results). Floats
are now tracked via a __float_names typed-binding set (parallel to the
existing int-tracking scheme) and arithmetic is emitted as real C double
ops.

Also fixes math_log, which was wrongly aliased to natural log (duplicating
math_ln) — now uses log10 — and adds the missing <math.h> include. Rebuilt
elc binary included.

lang/el-compiler/runtime/el_runtime.c

@@ -5327,8 +5327,8 @@ el_val_t str_to_float(el_val_t s) {
 /* ── Math (Float-aware) ──────────────────────────────────────────────────── */
 
 el_val_t math_sqrt(el_val_t f) { return el_from_float(sqrt(el_to_float(f))); }
-el_val_t math_log(el_val_t f)  { return el_from_float(log(el_to_float(f))); }
-el_val_t math_ln(el_val_t f)   { return el_from_float(log(el_to_float(f))); }
+el_val_t math_log(el_val_t f)  { return el_from_float(log10(el_to_float(f))); } /* base-10, per runtime/math.el */
+el_val_t math_ln(el_val_t f)   { return el_from_float(log(el_to_float(f))); }   /* natural log */
 el_val_t math_sin(el_val_t f)  { return el_from_float(sin(el_to_float(f))); }
 el_val_t math_cos(el_val_t f)  { return el_from_float(cos(el_to_float(f))); }
 el_val_t math_pi(void)         { return el_from_float(3.141592653589793238462643383279502884); }

lang/el-compiler/runtime/el_runtime.h

@@ -49,6 +49,7 @@
 
 #include <stdint.h>
 #include <stdlib.h>
+#include <math.h>   /* fmod, sin, sqrt, ... — used by codegen'd float arithmetic */
 
 typedef int64_t el_val_t;