terminal-pet --oneline for a prompt segment #13

terminal-pet only has a continuous redraw loop, so there is nothing to call once per prompt.

Measured on this Mac: 2.5ms per exec, 0.1ms to connect and read the cached snapshot — cheap enough for a synchronous powerlevel10k segment.

Done when:

• signal_client::Frames::snapshot() reads the last-value cache the daemon sends on connect and returns, without waiting out a timeout.
• terminal-pet --oneline prints one line — face plus keys/min — and exits. It prints nothing and exits non-zero when the daemon is not running, so a prompt segment can hide itself.