feat(relay): rendezvous-relay service — 7 packages + plans (contracts/transport/agent/control-plane/e2e/auth/web)

Multi-tenant reverse-tunnel service ("ngrok for Claude Code" with E2E): a
host-agent dials OUT to an operator-run relay; external devices reach the host
THROUGH the relay, routed by per-tenant subdomain, forwarding ciphertext only
(the relay never sees plaintext). Lets a customer reach their own self-hosted
web-terminal from anywhere with zero networking setup.

Packages — all tsc-strict + vitest green (656 tests), cross-package integration verified:
- relay-contracts: frozen shared contracts (mux frame codec, data model,
  capability token, E2E envelope, pairing) — the src/types.ts analog
- term-relay:   native WS mux + stateless data plane (subdomain routing, ciphertext forward)
- agent:        host-agent (pairing, per-host Ed25519 + mTLS dial-out, forwards to 127.0.0.1:3000)
- control-plane: accounts/hosts registry, pairing-code flow, routing table, provisioning
- relay-e2e:    browser<->agent E2E (X25519 ECDH through relay, AEAD, anti-replay, recoverable replay key)
- relay-auth:   Passkey/WebAuthn, capability tokens, per-host certs, deny-by-default tenant isolation
- relay-web:    browser login + Web Crypto E2E + client-side preview rendering

Security invariants INV1-15 enforced; cross-tenant isolation CI tripwire live
(.github/workflows/relay-tripwire.yml). Design + implementation-level plans in
docs/PLAN_RELAY_*.md and docs/EXPLORE_RELAY_SERVICE.md.

NOTE: generated autonomously per the reviewed plans. The security-critical
packages (relay-e2e, relay-auth) REQUIRE expert security audit before any real
deployment — passing tests prove self-consistency, not resistance to attackers.
Base app (src/, public/) unchanged; concurrent desktop work left uncommitted.

relay-auth/src/audit/alert.ts

@@ -0,0 +1,19 @@
+/**
+ * T14 · Audit-alert wiring. Turns the INV1 tripwire into a RUNTIME detector: a
+ * `cross-tenant-attempt` audit event fires an operator alert immediately (EXPLORE §4e HIGH). Alert
+ * payload carries metadata only (no terminal bytes, INV10).
+ */
+import type { AuditEvent } from '../types.js'
+
+export type AlertKind = 'cross-tenant' | 'revocation' | 'auth-anomaly'
+
+export interface Alerter {
+  fire(kind: AlertKind, e: AuditEvent): Promise<void>
+}
+
+/** Fires a `cross-tenant` alert on `action === 'cross-tenant-attempt'`; no-op otherwise. */
+export async function onAuditEvent(e: AuditEvent, alerter: Alerter): Promise<void> {
+  if (e.action === 'cross-tenant-attempt') {
+    await alerter.fire('cross-tenant', e)
+  }
+}