seam refusal + control tests: a runtime binding can short-circuit

Prediction 3 was FALSE. I expected refusal to be impossible through the seam
because the entry indirection discarded its return. One line:

    { el_val_t __s = el_seam_run(EL_STR(f), 0, 0); if (__s) return __s; }

work() returns 7; bound to a refusing construct AFTER the build it returns 42.
So three of the five compile-time kinds are runtime-bindable: entry injection,
exit injection, and refusal. wraps_body needs invocation control and
prohibits_outside is compile-time by nature.

104/104 native compiler tests pass.

lang/el-compiler/src/codegen.el

@@ -3208,7 +3208,7 @@ fn cg_entry_seam(stmt: Map<String, Any>, fn_name: String) -> Void {
     // RUNTIME SEAM: codegen cannot know which constructs will be bound to this
     // fn after the binary exists, so the indirection is unconditional. What
     // applies is resolved at execution against a table written later.
-    emit_line("  el_seam_run(EL_STR(" + c_str_lit(fn_name) + "), 0, 0);")
+    emit_line("  { el_val_t __s = el_seam_run(EL_STR(" + c_str_lit(fn_name) + "), 0, 0); if (__s) return __s; }")
     let gdl = stmt["decorators"]
     let n_gdl: Int = native_list_len(gdl)
     let gi = 0