The `omp grep` subcommand resolved its path argument with a bare
`path.resolve` in `runGrepCommand`, bypassing `expandPath`. The
leading-colon strip from #5529 never fired, so `:/abs/path` was
mangled into `<cwd>/:/abs/path` and failed to resolve.
Route the path arg through `expandPath` so it inherits the leading-`:`
strip plus `@`-prefix, tilde, and unicode-space normalizations, matching
`read`/`edit`/in-agent `grep`.
Fixes#5624
roboomp
e291d77cb0