feat: implement CookieBridge M1 — core protocol & relay server

- Protocol spec: encrypted envelope format, device identity (Ed25519 + X25519),
  LWW conflict resolution with Lamport clocks
- E2E encryption: XChaCha20-Poly1305 via sodium-native, X25519 key exchange
- WebSocket relay server: stateless message forwarding, device auth via
  challenge-response, offline message queuing, ping/pong keepalive
- Device pairing: time-limited pairing codes, key exchange broker via HTTP
- Sync protocol: envelope builder/opener, conflict-resolving cookie store
- 31 tests passing (crypto, pairing, conflict resolution, full integration)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

vitest.config.ts

@@ -0,0 +1,8 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    globals: true,
+    testTimeout: 15_000,
+  },
+});