Introduce a per-key `text_command` + `refresh` feature: the service
periodically runs a shell command and renders its stdout as the key's
text overlay, compositing over the base icon (or a black background for
text-only keys) each tick. `text` acts as the static fallback shown
before the first run or when the command errors/outputs nothing. A
refresh goroutine owns the key's image and also handles an optional poll
block (choosing icon_true/icon_false per tick). Adds `$(...)` sugar in
`text` as shorthand for `text_command`.
- internal/config: add TextCommand/Refresh fields to KeyConfig
- cmd/streamdeck: refreshTextKey goroutine, runTextCommand, unwrapCmdSubst
- config.example.yaml: document the feature with a `flow` pomodoro
live-countdown example (status --short, toggle/skip/stop/gui)
- modules.example.yaml: example config updates
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TEoLyNbtbjbDq7aTWAymUG
