fix(trail): tell tune not to cite gathered-only refs in templates

The gathered signal includes PR/issue titles and numbers, and the model was baking references like "(PR #77)" / "(issue #67)" into the rewritten templates. But at eval time the runner only sees the diff — it has no access to PRs, issues, or repo history — so those citations are inert at best and can nudge the runner to emit meaningless references. Add a tuning guideline to fold such lessons in as generic, diff-checkable criteria instead of citing issue/PR numbers or commit hashes.