Feature request: Command button type for displaying shell command output #82

I've been using tiny-dfr as a system monitor on my 2018 MacBook Pro — showing CPU/GPU temps, fan speed, RAM usage, etc. on the touch bar. To do this I added a Command button type that runs a shell command periodically and displays the stdout as text.

How it works:

Config example:

PrimaryLayerKeys = [
    { Command = "/etc/tiny-dfr/cpu-status.sh", Interval = 3, Stretch = 3 },
    { Command = "cat /proc/loadavg | awk '{print $1}'", Interval = 5, Stretch = 2 },
]

• Command — shell command run via /bin/sh -c
• Interval — refresh interval in seconds (default 5)
• Renders like a Text button, just centered stdout output
• On error or timeout (3s), displays "—"

Implementation is pretty minimal:

• Two new fields on ButtonConfig (command, interval)
• A ButtonImage::Command variant storing the command, interval, cached output, and last-run timestamp
• Refresh logic in the main loop similar to the existing time/battery refresh
• displays_commands flag on FunctionLayer like displays_time/displays_battery

Commands run after privilege drop so they execute as nobody — fine for /proc, /sys, sensors, etc. Execution is synchronous with a 3s timeout so a hung command won't freeze the bar permanently.

I have a working implementation on my fork if there's interest. Wanted to check if this is something you'd consider merging before cleaning it up into a proper PR.

Branch: https://github.com/Pilves/tiny-dfr/tree/feature/command-button

This issue was drafted with Claude Code.