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.

.github/workflows/relay-tripwire.yml

@@ -0,0 +1,30 @@
+# PERMANENT cross-tenant isolation tripwire (INV1) — see docs/PLAN_RELAY_AUTH_ISOLATION.md T13.
+#
+# This job MUST be a REQUIRED status check. A green build is impossible if cross-tenant isolation
+# regresses (device A reaching host B). DO NOT delete, skip, or make this non-required. If it ever
+# goes red, BLOCK the merge (CRITICAL per code-review.md).
+name: relay-tripwire
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  cross-tenant-tripwire:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: relay-auth
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+      - name: Install relay-auth (+ local relay-contracts)
+        run: npm install
+      - name: Strict typecheck
+        run: npx tsc --noEmit
+      - name: THE cross-tenant tripwire (A -> B must be 403)
+        run: npx vitest run tripwire/cross-tenant
+      - name: Full relay-auth suite
+        run: npx vitest run