`preevy exec`

Need a way to execute commands in a container, for debugging and troubleshooting.

I suggest the syntax `preevy exec [--[no-]tty] [--[no-]interactive] [command]`

All the flags from the `urls` command should be present (`--id, --tunnel-url` etc.)

Pipe `stderr` and `stdout` to calling process.

Should support interactive (`stdin` from calling process) or one-shot.

Start by locating the existing `urls` command and its `--id` and `--tunnel-url` handling, then trace how commands are executed in containers. Implement the `preevy exec` syntax with matching flags, optional TTY and interactive stdin, and stdout/stderr forwarding. Done means both interactive and one-shot commands work against a selected service.

Written by the indexing model from the issue text.