docs: remove residual TCFS frontier drift

[Jesssullivan]

Summary

Refresh residual TCFS frontier docs after #513/#529/#534/#537 so the current stop rule is consistent across older packets and runbooks.

Changes

• mark PR-4/tcfs: loser-side no-loss guard for git keep-both (TIN-2552) #534 as merged but still deploy/canary pending
• soften PZM language from hardware/Finder healthy to not accepted for TCFS offload until lab gates pass
• move key-rotation language from closed Evidence rescue: uncommitted roam-canary / large-workdir packets expected by PR #514 #517/TIN-1899 to TIN-2551
• supersede old G5-git-5 expected-red wording with post-tcfs: loser-side no-loss guard for git keep-both (TIN-2552) #534 deploy/canary gating

Test plan

• git diff --check
• targeted stale-phrase grep over docs/ops and divergent keep-both canary plan
• task test passes locally — not run; docs-only, and neo-local heavy builds are intentionally avoided
• task lint passes locally — not run; docs-only, and neo-local heavy builds are intentionally avoided
• Verified affected functionality manually

Checklist

• Docs updated
• CHANGELOG.md updated (not applicable)
• No secrets or credentials in diff

Linear: TIN-1620, TIN-2552, TIN-2551