docs: refresh sustained replay and retirement status

[kim-em]

Summary

• replace the stale single-run replay description with the current sustained two-lane state
• record that repeated exact-packet public/private terminals, cleanup, and one-successor invariants pass
• record that final-delta and Issue-retirement drafts now include the matching leaderboard copy change

This updates current status in place and does not add a run history or change product scope.

Validation

• git diff --check: clean
• public: three consecutive monitored terminal continuations verified; latest queue 157 queued / 16 accepted / 1 safely failed, with one successor
• private: three sustained terminal runs verified accepted with complete source/credential/artifact/executor cleanup; latest queue 626 with one successor
• protected submissions main and both controllers remain exact d26a3090a338358915cc94651ec7efddde71d241