feat: add --quiet flag to cli for suppressing output

[amoeba]

Adds a global CLI flag, --quiet (-q for short) that, when set, completely suppresses output (i.e., stdout). Also includes updates to keep the docs in sync.

Command line tools use a variety of methods to enable/disable or enhance/reduce output and there's not really a clear best way to do this. The GNU standard suggests --quiet and for the flag to suppress "usual" output. curl takes a different approach with --silent which means "print just my final results, not any progress". uv uses -q to reduce output and -qq to completely disable output.

This does not include tests because I think it would add quite a bit of noise for not much gain.

Closes #202

[amoeba]

For reviewers, if we wanted to go the uv route with -q/-qq,

• -q could suppress bubbletea output and only print what we call "final" output
• -qq could then suppress all output, bubbletea and final

[zeroshade]

LGTM just needs the addition to the shell completion scripts