[Bug]: Format scripts hiding errors when using grep from busybox

### What happened?

`format.sh` uses `grep -vFxf <(git ls-files --deleted)` to exclude deleted files from the formatter input. When `git ls-files --deleted` returns nothing (normal for a clean checkout), the pattern file is empty. BusyBox `grep -vFxf ` with an empty pattern file exits 1 and produces no output, where GNU grep passes all lines through. The `|| true` swallows the exit code but not the lost output, leaving files="" for every language — so no formatter ever runs.

### Version

Development (host) and target OS/architectures:

Output of `bazel --version`:

Version of the Aspect rules, or other relevant rules from your
`WORKSPACE` or `MODULE.bazel` file:

Language(s) and/or frameworks involved:

### How to reproduce

```shell

```

### Any other information?

_No response_

Start in format.sh and inspect the grep -vFxf process substitution that filters git ls-files --deleted. Reproduce it with BusyBox grep on a clean checkout, then verify that formatter input still includes all relevant files and that formatters run normally when the deleted-file list is empty.

Written by the indexing model from the issue text.