Make the driver rule explicit

- CBD net positive and THC net positive → Balanced
- Only CBD net positive → CBD-forward
- Only THC net positive → THC-forward
- Neither ligand recorded → Insufficient driver evidence
- Both net negative → Both contraindicated
- Conflicting or tied evidence → Indeterminate/conflicting evidence

No files are listed in the issue. Start by locating where the CBD/THC net-positive/net-negative driver decision is computed and how it maps to output labels. Implement the six-case rule explicitly in that branch, then find or add tests for driver classification to cover each listed input combination and confirm each produces the stated result.

Vom Indexierungsmodell aus dem Issue-Text verfasst.