docs(fix-issue): ship every defect a run proves instead of listing it as not in this PR

[datlechin]

Summary

• A run fixes every defect its lanes or reviewers prove, wherever it sits, instead of listing pre-existing ones under "Not in this PR".
• A defect in another app ships in a second PR from the same run, under that app's profile.
• A trade-off with no fix that holds both sides is a product decision to ask about, not a reason to leave the defect.
• Only a step a run must never take (library or plugin publish, CloudKit deploy, tag) is left for the maintainer, under "Needs the maintainer".
• Review repeats until a round finds nothing real; a fourth round with new defects in the change's own code sends the run back to the plan.
• The hunt lane brief says findings ship in this run, not only this PR.

Test plan

• Docs only: scripts/check-banned-words.sh --staged clean.