Move C stdlib headers before local/project headers with a
blank line separator, matching the AGENTS.md include order rule.
Replace em dash with colon in main.c comment.
Replace log_message with log_debug/info/warn/err and a level filter
controlled by logger_set_level. Extract the printf sink into
log_write so CMock can intercept it in test_logger. Add 9 tests
covering emit and suppression behaviour per level.
portersky