014 for template cross target

// Cross-target `for(0..3)` with a `print` effect-handler body. Pins the whole
// chain lowering identically to Zig and JS:
//   - `for|template|js` (koru_std/control.kz) is selected on a --lang=js build;
//   - the range iterable `0..N` lowers to a JS counting loop
//     (`for (let i = 0; i < N; i++)`) via `parse_range` (template_processor.zig),
//     not a verbatim `for (… of 0..N)` that node would reject;
//   - the `! each` effect splice binds the item and runs the handler body; and
//   - that handler body — `std/io:print(...)`, a comptime|transform nested as an
//     effect-splice body — lowers through its `|js` variant, spliced by the JS
//     emitter from the invocation's `inline_body`, not emitted as a `.impl` call.
// A JS-array iterable (`for([1,2,3])`) rides the same path as a `for…of`.
~import std/control
~import std/io

~for(0..3)
! each _ |> std/io:print("tick\n")
| done |> _