- Add _json_formatter.py: structured NDJSON output with timestamp, level,
  logger, message, context fields, exception, and extra (bound context)
- Add _host_config.py: warn when host.json logLevel.default is more
  restrictive than the configured setup_logging() level
- Add format parameter to setup_logging() accepting 'color' (default)
  or 'json' for local development output format
- Add nosec B110 annotations to intentional try/except/pass blocks
  in _context.py (Design Principle 3)
- Export JsonFormatter in public API, bump version to 0.2.0
- Add comprehensive tests (10 new tests, 42 total)
- Update README, DESIGN.md, and PRD.md for v0.2.0 features