feat: add Math.sin, Math.cos, Math.atan2 trig functions

Adds trigonometric functions to the Math module across interpreter,
type system, and C backend. JS backend already supported them.
Also adds #include <math.h> to C preamble and handles Math module
calls through both Call and EffectOp paths in C backend.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types.rs

@@ -1887,6 +1887,18 @@ impl TypeEnv {
                 "round".to_string(),
                 Type::function(vec![Type::var()], Type::Int),
             ),
+            (
+                "sin".to_string(),
+                Type::function(vec![Type::Float], Type::Float),
+            ),
+            (
+                "cos".to_string(),
+                Type::function(vec![Type::Float], Type::Float),
+            ),
+            (
+                "atan2".to_string(),
+                Type::function(vec![Type::Float, Type::Float], Type::Float),
+            ),
         ]);
         env.bind("Math", TypeScheme::mono(math_module_type));