Move Config struct to internal/config with exported fields. Replace
global var config with package-level cfg pointer. Add OpenLogFile to
config package. Add type alias Config = appconfig.Config in main
package for backward compatibility.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Remove unused global var `in`, func `strout`, func `echoConsoleInput`,
func `padRight`, func `ErrorP`, and func `ErrorF`. Inline error check
in CloseSerial. Add COM.exe and coverage.out to .gitignore.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>