fix: document strtold cbindgen trailer (no Rust impl needed)

strtold is declared via cbindgen trailer section as 'long double'.
No Rust implementation required — linker resolves via compat lib.

src/header/stdlib/mod.rs

@@ -1507,7 +1507,9 @@ pub unsafe extern "C" fn strtol(s: *const c_char, endptr: *mut *mut c_char, base
     strto_impl!(c_long, true, c_long::MAX, c_long::MIN, s, endptr, base)
 }
 
-// TODO: strtold(), when long double is available
+// TODO: strtold(), when long double is available.
+// Declared via cbindgen trailer section (long double strtold(...)) for
+// C++ <cstdlib> compat. Linker resolves via libredbear-qt-strtold-compat.so.
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strtol.html>.
 #[unsafe(no_mangle)]