fix: separate worker.log and launchd_stderr.log responsibilities

[nonz250]

Summary

Give worker.log and launchd_stderr.log distinct responsibilities. Today every log line goes to both, so launchd_stderr.log is a full duplicate of the worker log and grows just as fast.

Problem

createLogger() in src/worker/logger.ts writes each formatted line with console.error and also appends it to worker.log. Under launchd, stderr is redirected to launchd_stderr.log, which nothing rotates or trims.

Confirmed on a live installation: worker.log at 7.4 MB and launchd_stderr.log at 7.4 MB holding the same content - roughly 15 MB for four months, half of it redundant.

Scope

• worker.log holds the application log.
• launchd_stderr.log holds only what the logger cannot capture: uncaught exceptions, unexpected child-process output, and failures that happen before the logger is configured.
• Keep console output for interactive runs (npm run dev:worker), for example when no log directory is configured or when stderr is a TTY.

Considerations

• Startup failures before configureLogger() runs - a config.yml that fails to load stops every repository - currently reach stderr only. That path has to keep working, since it is the sole signal that the worker stopped entirely.
• Touches the same file as fix: worker.log is never rotated and grows without bound #111, so the two should land in sequence rather than in parallel.