Adds the Engineer component that polls for ready merge-requests and
processes them according to the merge queue design.
Features:
- Main loop that queries `bd ready` for merge-request type issues
- Configurable poll_interval and max_concurrent from rig config.json
- Graceful shutdown via context cancellation or Stop() method
- Claims MRs via `bd update --status=in_progress` before processing
- Handles success/failure with appropriate status updates
Configuration (in rig config.json merge_queue section):
- poll_interval: duration string (default "30s")
- max_concurrent: number (default 1)
- enabled, target_branch, run_tests, test_command, etc.
Also adds ReadyWithType() to beads package for type-filtered queries.
Note: ProcessMR() and handleFailure() are placeholders - full
implementation in gt-3x1.2 and gt-3x1.4.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
