Problem:
- Dot-repeat of a Visual selection prepared by a `<Cmd>` mapping,
results in E1255 and leaves Visual mode active.
- Visual-mode capture is implemented as a second, parallel "capture
engine": it re-composes a CmdSpec from cmdarg_T per key and decides
replayability from its own table of "void" key classes.
Solution:
- Model nested `normal_execute()` as a `CmdFrame` stack,
instead of a single module-scoped `stage`.
- Capture `<Cmd>` ":norm …" commands as subatoms from its nested frames.
- Produce every command exactly once; atom_push_raw() routes the atom to
the Visual composite while a selection is open, like it already does
for mapping composites.
- `v/pat<CR>d` is now repeatable and cascades.