Add 'gt mq retry <rig> <mr-id>' command to retry failed MRs:
- Added GetMR() and Retry() methods to refinery.Manager
- Added RegisterMR() for persistent MR tracking
- Added PendingMRs field to Refinery state
- Created new mq.go command file with retry subcommand
- Support --now flag for immediate processing
- Added comprehensive tests for retry functionality
Closes gt-svi.4
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>