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-e2e/test/vectors/aead.json

@@ -0,0 +1,20 @@
+[
+  {
+    "alg": "aes-256-gcm",
+    "key": "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
+    "nonce": "101112131415161718191a1b",
+    "aad": "633268",
+    "plaintext": "72656c61792d653265204b415420706c61696e746578742030313233343536373839",
+    "ciphertext": "0f9bf47730e45f81af55435c5b59193fb639207a7eba2391d7c8d0546a6162ec68d0",
+    "tag": "1125e02e1f595a027122eba5cc4e640a"
+  },
+  {
+    "alg": "xchacha20-poly1305",
+    "key": "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
+    "nonce": "101112131415161718191a1b1c1d1e1f2021222324252627",
+    "aad": "633268",
+    "plaintext": "72656c61792d653265204b415420706c61696e746578742030313233343536373839",
+    "ciphertext": "56996f972da544e1f3a2698ca9b053606ee2999b9c1554f3d675cb452e1096a292ee",
+    "tag": "a7b4abef56829d16df973d0a954f08d2"
+  }
+]

relay-e2e/test/vectors/envelope.json

@@ -0,0 +1,7 @@
+{
+  "seq": "42",
+  "wire": "000000000000002a0c000000111000000000000000000000002a79a800de55c674011c4d0c27e5f3ec51f993d647d16355bd686822cde82bd5b343",
+  "nonce": "00000000000000000000002a",
+  "ciphertext": "79a800de55c674011c4d0c27e5f3ec51f9",
+  "tag": "93d647d16355bd686822cde82bd5b343"
+}

relay-e2e/test/vectors/fingerprint.json

@@ -0,0 +1,4 @@
+{
+  "agentPubkey": "404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f",
+  "enrollFpr": "sha256:yipP5yf6rs8W7NEwqG4IhcVUDAU3U0BEUHHAZXVV_UI"
+}

relay-e2e/test/vectors/hkdf.json

@@ -0,0 +1,8 @@
+{
+  "sharedSecret": "abababababababababababababababababababababababababababababababab",
+  "clientNonce": "0101010101010101010101010101010101010101010101010101010101010101",
+  "hostNonce": "0202020202020202020202020202020202020202020202020202020202020202",
+  "master": "2949dafdb8800efa58bb2c7b8808c774e03aa581e02f1030f7233f381cbacab2",
+  "c2h": "48cb497e84fb28d514479f7c6b3b7017b9db89db589168c57df456a270d8bf50",
+  "h2c": "4184fe15fa77fbfda17ea39925ad6d2ca03d6cc225eacd637b45dafceed2f2f4"
+}