docs: current-state the bitcoin multi-version design; move its rollout handoff local

bitcoin-multi-version-design.md carried three layers of stale internal content:
an 80-line HTML-comment work-tracking block (per-phase status with "UNCOMMITTED
on the branch", node numbers, "Next action when resuming", "Decisions still
needed from user"); a rendered "Status: design (2026-06-22)" header that was
wrong — the feature shipped, all four phases, with the downgrade guard added
today; two private `MEMORY →` references; and a node-numbered scheduling note.

Now: the comment block is gone, the status reflects reality, the MEMORY
references and node numbers are removed, and "verify on a real node" replaced
the specific fleet addresses. The design content (source-of-truth decision,
phase designs, invariants) is unchanged.

Separately, bitcoin-version-bulletproof-rollout.md was an inter-agent rollout
handoff — node numbers, branch coordination, "the other agent owns" — not a
design or reference doc. Moved to local-only (still on disk, gitignored) like
the other handoffs; its two path references (a plan doc and a script comment)
are generalized.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitignore

@@ -141,3 +141,4 @@ uploads/
 /docs/security/ENTROPY-SEED-AUDIT-2026-07-31.md
 /image-recipe/INTEGRATION-GUIDE.md
 /docs/multinode-testing-plan.md
+/docs/bitcoin-version-bulletproof-rollout.md