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.

term-relay/mux/frame-codec.ts

@@ -0,0 +1,28 @@
+/**
+ * T2 · Mux frame codec (§4.1) — the 15-byte header + opaque payload, and the CBOR/int
+ * control-frame payload codecs.
+ *
+ * The binary codec is FROZEN in `relay-contracts` (INDEX §4.1, OQ2 resolved: the codec ships
+ * in contracts so P1 relay and P2 agent share ONE encoder). P1 re-exports it as the stable
+ * `mux/` surface that T6 (mux-session) and the data plane consume, adding NO wire behavior.
+ *
+ * Security (INV2/INV11): this module imports NO terminal/ANSI parser. DATA payloads are opaque
+ * `Uint8Array` and are never inspected here; only OPEN/WINDOW_UPDATE/GOAWAY control frames are
+ * shape-validated (via the contracts' Zod guards).
+ */
+export {
+  MUX_HEADER_BYTES,
+  MUX_VERSION,
+  encodeMuxFrame,
+  decodeHeader,
+  decodeMuxFrame,
+  encodeOpen,
+  decodeOpen,
+  encodeWindowUpdate,
+  decodeWindowUpdate,
+  encodeGoaway,
+  decodeGoaway,
+} from 'relay-contracts'
+
+export { TYPE_TO_BYTE, BYTE_TO_TYPE } from './type-bytes.js'
+export type { MuxFrameType, MuxFrameHeader, MuxOpen, GoAwayReason } from 'relay-contracts'