fix(resolve): seed trunc builtin in resolver context (#135)

`trunc` is a genuine runtime builtin (interp.ml:674, kernel_sublang
builtin set) but was absent from the resolver's builtin-seed list while
its siblings floor/ceil/round are present, so math.affine failed
resolution with UndefinedVariable "trunc". Add `def "trunc"`.

Verified on origin/main @651cc12: math.affine now passes the resolve
stage (its remaining Int/Float TypeMismatch is a separate pre-existing
math.affine typecheck issue, out of scope). Full stdlib sweep 11/8 →
11/8, zero regression.

Refs #128

Author: hyperpolymath

lib/resolve.ml

@@ -64,6 +64,7 @@ let create_context () : context =
   (* Numeric coercions and math *)
   def "int"; def "float";
   def "sqrt"; def "cbrt"; def "pow_float"; def "floor"; def "ceil"; def "round";
+  def "trunc";
   def "abs"; def "max"; def "min";
   def "sin"; def "cos"; def "tan"; def "atan"; def "atan2";
   def "exp"; def "log"; def "log10"; def "log2";