Wallet-verified member messaging (matrix-lines permissions, admin visibility)

- messages.js: challenge/personal_sign/recover auth (vendored pinned
  js-sha3 0.9.3 + noble-secp256k1 1.7.1, server-side only; self-tested
  positive + tamper cases), 30d HttpOnly sessions, message store on the
  volume, matrix-line permissions (your downline direct or broadcast, your
  upline chain - nothing else, so spam is impossible by construction),
  daily rate limits (30 direct / 3 broadcasts), 1500-char plain text
- chain.js: memberIdByAccount (wallet -> position for sign-in)
- API: msg-challenge/-verify/-me/-inbox/-send/-read public + msg-unread
  (count only, no auth) + admin/messages (full visibility, disclosed to
  members in the UI)
- Dashboard: Messages card with unread bell, one-tap wallet sign-in,
  inbox with auto-read, compose with to-ID or whole-team broadcast
- Admin: Member Messages review table
- Chatbot canned answer + AI system prompt updated

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

chain.js

@@ -667,6 +667,15 @@ function getOrgShare(rootId) {
   };
 }
 
+// Wallet address -> position id (for wallet-verified messaging sign-in).
+// One position per address by contract design.
+function memberIdByAccount(address) {
+  if (!state || !address) return null;
+  const a = String(address).toLowerCase();
+  for (const [id, m] of Object.entries(state.members)) if (m.account === a) return Number(id);
+  return null;
+}
+
 // Company-rotation pick: breadth-first (matrix order, left→right) first
 // position under `rootId` that still needs directs — the "next open team
 // position" for the public rotation when publicRotationMode==='chain'.
@@ -735,4 +744,4 @@ async function getIncome(id) {
   };
 }
 
-module.exports = { startIndexer, getPayoutsPublic, verifyMember, memberLookup, memberPublic, getIncome, getOwnerUpgradeNeeds, getOrgRouting, getOrgShare, getCoachingScan, getMatrixTree, isInTeam, nextOpenPosition, balanceOf, CONTRACT };
+module.exports = { startIndexer, getPayoutsPublic, verifyMember, memberLookup, memberPublic, getIncome, getOwnerUpgradeNeeds, getOrgRouting, getOrgShare, getCoachingScan, getMatrixTree, isInTeam, nextOpenPosition, memberIdByAccount, balanceOf, CONTRACT };