feat: add n8n serve node and harden remote access

- Add the n8n community node package with credentials, command mapping, direct serve TCP client, and browser-cli protocol crypto helpers.

- Cover Ed25519 signing, canonical JSON, PQ transport encryption, request mapping, and security behavior with unit tests.

- Harden serve-http with per-address rate limiting, an 8 MB request body cap, and clear warnings when binding plain HTTP beyond loopback.

- Stop one-shot --key overrides from being persisted automatically; document explicit remote trust and keep key-management behind the keys policy tier.

- Make HTML-to-Markdown conversion safer by bounding tree depth and dropping unsafe link/image URL schemes.

- Bump package and extension release metadata to 0.16.3.

tests/test_new_feature_commands.py

@@ -357,6 +357,48 @@ def test_serve_http_uses_compare_digest():
   assert "compare_digest" in src
   assert "== f\"Bearer" not in src
 
+def test_serve_http_rate_limiter_blocks_when_exhausted():
+  """A burst-1 limiter lets the first request through, then sends 429."""
+  from browser_cli.commands.serve_http import _Handler
+  from browser_cli.serve.security import RateLimiter
+
+  handler = _Handler.__new__(_Handler)
+  handler.client_address = ("203.0.113.5", 5000)
+  handler.rate_limiter = RateLimiter(rate=0.001, burst=1)
+  sent = []
+  handler._send = lambda status, payload: sent.append((status, payload))
+
+  assert handler._within_rate_limit() is True
+  assert handler._within_rate_limit() is False
+  assert sent and sent[-1][0] == 429
+
+def test_serve_http_rate_limiter_none_never_limits():
+  from browser_cli.commands.serve_http import _Handler
+
+  handler = _Handler.__new__(_Handler)
+  handler.client_address = ("203.0.113.5", 5000)
+  handler.rate_limiter = None
+  assert all(handler._within_rate_limit() for _ in range(100))
+
+def test_serve_http_default_rate_limit_active():
+  from browser_cli.commands.serve_http import _Handler
+
+  with patch("browser_cli.commands.serve_http.BrowserCLI"), \
+       patch("browser_cli.commands.serve_http.ThreadingHTTPServer") as server_cls:
+    server_cls.return_value.serve_forever.side_effect = KeyboardInterrupt
+    CliRunner().invoke(main, ["serve-http", "--no-auth"])
+  # The handler class passed to the server carries an active RateLimiter by default.
+  handler_cls = server_cls.call_args.args[1]
+  assert handler_cls.rate_limiter is not None
+  assert handler_cls.rate_limiter.rate == 100.0
+
+def test_serve_http_non_loopback_warns_about_cleartext():
+  with patch("browser_cli.commands.serve_http.BrowserCLI"), \
+       patch("browser_cli.commands.serve_http.ThreadingHTTPServer") as server_cls:
+    server_cls.return_value.serve_forever.side_effect = KeyboardInterrupt
+    result = CliRunner().invoke(main, ["serve-http", "--host", "0.0.0.0", "--token", "x"])
+  assert "clear text" in result.output
+
 def test_command_policy_allow_all_grants_everything():
   policy = command_policy_from_options(
     allow_read_page=False, allow_control=False, allow_dangerous=False, allow_all=True