test(relay): cross-package e2e adversarial security harness

New e2e/ package wires the REAL P5(auth)+P4(crypto)+P2(agent) exports through
in-memory seams and an untrusted-relay attacker vantage (RelaySpy). Dynamically
re-validates F1–F4/F6 plus MITM/reflection/replay/reorder/INV2/cross-tenant/
single-use — every assertion runs the production code path. 21 tests green, tsc
clean. node_modules via symlinks (gitignored); no npm install needed.

e2e/vitest.config.ts

@@ -0,0 +1,8 @@
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+  test: {
+    include: ['tests/**/*.test.ts'],
+    environment: 'node',
+  },
+})