Add three built-in molecule definitions that are automatically seeded
during `gt install`:
- engineer-in-box: Full workflow from design to merge (5 steps)
- quick-fix: Fast path for small changes (3 steps)
- research: Investigation workflow (2 steps)
These molecules provide reusable workflow templates that polecats can
instantiate to execute multi-step procedures with proper dependency
tracking between steps.
Closes gt-4nn.4
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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