feat: Add auto-refresh support to TUI model

feat: Add configurable color presets and config loader

Add internal/config to load user presets from a platform-aware config.yaml and use them in the TUI (falling back to
built-in presets if absent). Add docs/config.example.yaml and README instructions. Add gopkg.in/yaml.v3 dependency and
ignore the built 'lifx' binary. Also update a few internal types/usages (map[string]any and logging variadic types) and
minor UI formatting tweaks.

Update README.md