moltenhub-layer out logging levels with config.json defaults

[jefking]

Summary

• add explicit hub log levels (error, warn, info, debug) with canonical parsing/validation
• add log_level to hub init/runtime config handling with default info
• backfill missing log_level in runtime config.json and preserve configured values across runtime config writes
• add leveled hub log routing in cmd/harness so noisy command/progress lines are treated as debug while preserving task-log mirroring
• route hub UI/PR monitor logs through the same leveled logger
• update docs/example config and add focused tests

Validation

• go test ./...