Add pino-based logger module for production observability:
- JSON output to stdout for log aggregators (Loki, ELK)
- Configurable via LOG_LEVEL environment variable (defaults to "info")
- Log levels: error, warn, info, debug
- Error objects serialized with type, message, and stack trace
- Child logger support for bound context
- ISO 8601 timestamps in all log entries
Test coverage: 16 tests covering JSON format, log levels, error
serialization, and child loggers.
Total tests now: 553 passing across 31 test files.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
