feat(us-017): P2P gossip, NAT-traversal relay node, and TLS

- packages/p2p: identity (peer_id from sha256 of RSA pubkey), TLS cert
  generation with SHA-256 fingerprint, GossipClient (WSS PubSub with
  per-topic handlers, dedup by msg_id, auto-reconnect), MdnsDiscovery
  (zeroconf optional dependency, graceful no-op fallback)
- packages/relay: new meshnet-relay package — RelayServer (asyncio +
  websockets) with gossip fanout hub, circuit relay proxy for NAT traversal,
  peer registry; meshnet-relay CLI
- packages/p2p/relay_bootstrap.json: team relay bootstrap list
- Tracker: _NodeEntry gains relay_addr, cert_fingerprint, peer_id; both
  register and heartbeat handlers read and store these optional fields
- docs/adr/0010 already written (previous commit)
- conftest.py: packages/relay added to sys.path
- 18 new tests; 115 passed total, 1 skipped (no regressions)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/p2p/pyproject.toml

@@ -8,6 +8,14 @@ version = "0.1.0"
 description = "Distributed Inference Network gossip and shard swarm"
 requires-python = ">=3.10"
 
+dependencies = [
+    "cryptography>=41",
+    "websockets>=13",
+]
+
+[project.optional-dependencies]
+mdns = ["zeroconf>=0.131"]
+
 [tool.setuptools.packages.find]
 where = ["."]
 include = ["meshnet_p2p*"]