redirection to file descriptors

Missing implementation for non-real-file redirections:

```sh
command >&2
command 1>&2
command 2>&1
```

Currently these redirect to literal files like `&1`and `&2`.

These must be directly after the redirection operator, without spaces. `&` will be used for background processes in future so to redirect into a file containing that character we must use quotes.

Locate the shell code that parses and executes redirection operators, then trace how the characters after `>` are interpreted. Implement handling for the shown file-descriptor forms without spaces, while preserving quoted `&` and numeric text as filenames; verify each example no longer redirects to a literal `&1` or `&2` file.

Written by the indexing model from the issue text.