In the app-server debug client, allow redirecting output to a file in
addition to just stdout. Shell redirecting works OK but is a bit weird
with the interactive mode of the debug client since a bunch of newlines
get dumped into the shell. With async messages from MCPs starting it's
also tricky to actually type in a prompt.
## Summary
In an effort to start simplifying our sandbox setup, we're announcing
this approval_policy as deprecated. In general, it performs worse than
`on-request`, and we're focusing on making fewer sandbox configurations
perform much better.
## Testing
- [x] Tested locally
- [x] Existing tests pass