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.

examples/0614-comptime-reify-enum.sx

@@ -8,7 +8,7 @@
 #import "modules/std.sx";
 #import "modules/std/meta.sx";
 
-E :: reify(.enum(.{ name = "E", variants = .[
+E :: define(declare(), .enum(.{ name = "E", variants = .[
     EnumVariant.{ name = "value",  payload = i64  },
     EnumVariant.{ name = "closed", payload = void },
 ] }));

examples/0615-comptime-reify-typefn-identity.sx

@@ -9,7 +9,7 @@
 #import "modules/std/meta.sx";
 
 Box :: ($T: Type) -> Type {
-    return reify(.enum(.{ name = "Box", variants = .[
+    return define(declare(), .enum(.{ name = "Box", variants = .[
         EnumVariant.{ name = "some", payload = T    },
         EnumVariant.{ name = "none", payload = void },
     ] }));