Prune root docs: drop REVIEW.md, merge CORAL twins, PLAN.md -> ROADMAP.md

Root-doc audit follow-through:

- REVIEW.md deleted — a response memo to a past review whose asks all
  shipped (arbiter deployed, reference binding); nothing linked to it
- CORAL-IMPLEMENTATION.md merged into CORAL.md and deleted — two
  1,000-line docs answering the same question were guaranteed to drift.
  CORAL.md absorbed the unique parts: the verifier-gated round flow in
  §6 (policy checks, VERIFY/VERIFIED leg, ledger persist — the flow
  validated live on devnet), a verifier-agent row + harness note in the
  §3 agent table, and custody-model bullets in §7 (harnesses never hold
  keys, the policy choke point, the devnet guard)
- PLAN.md renamed to ROADMAP.md with a shipped-status banner — all six
  phases are done and live-validated, so a root file named PLAN read as
  "unfinished"; it is the build record + stretch list now
- TXODDS.md: editor table reformat (whitespace only)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: trilltino