green: erase the sx reify sugar — declare/define are the only constructors

Per the directive to strip reify entirely: the sx `reify(info)` one-shot is
removed. `define(handle, info)` now RETURNS the (completed) handle, so the
one-shot constructor chains as a single expression:
    T :: define(declare(), .enum(.{ name = "T", variants = ... }));

- meta.sx: drop reify; RecvResult/TryResult use `define(declare(), …)`.
- interp .define returns the handle type_tag (was void); call.zig lowers it
  with `Type` result and sets the info arg's target type to TypeInfo so the
  intercepted call still infers the `.enum(…)` literal.
- returnExprMintsType: a type-fn body that returns `define(…)` (or a bodied
  non-generic Type-returning sx helper) is comptime-evaluated.
- examples 0614 (direct) + 0615 (type-fn) use `define(declare(), …)`.

Full suite green (673). Files/docs still carry the old reify naming — the
rename sweep is the next commit.

src/ir/interp.zig

@@ -2062,7 +2062,8 @@ pub const Interpreter = struct {
             .nominal_id = cur.tagged_union.nominal_id,
         } };
         tbl.replaceKeyedInfo(handle, full);
-        return .{ .value = .void_val };
+        // Return the handle so the one-shot form chains: `T :: define(declare(), info)`.
+        return .{ .value = .{ .type_tag = handle } };
     }
 };