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_markdown_security.py

@@ -0,0 +1,50 @@
+"""Security/robustness tests for the HTML→Markdown converter on hostile page content."""
+from browser_cli.markdown.html import _MAX_TREE_DEPTH, convert_html_to_markdown
+from browser_cli.markdown.render import render_markdown
+
+def _identity(markdown):
+  return markdown
+
+# ── depth-bounded recursion (Finding 4: HIGH/DoS) ─────────────────────────────────
+
+def test_deeply_nested_html_does_not_crash():
+  """Thousands of nested elements must not raise RecursionError."""
+  depth = 5000
+  html = "<div>" * depth + "deep content" + "</div>" * depth
+  out = convert_html_to_markdown(html, _identity)
+  assert "deep content" in out  # text preserved despite flattening
+
+def test_deeply_nested_via_render_markdown_entrypoint():
+  html = "<div>" * 3000 + "x" + "</div>" * 3000
+  out = render_markdown(html)  # routes HTML through the converter
+  assert "x" in out
+
+def test_nesting_within_cap_is_preserved_structurally():
+  # A modest list nesting (well under the cap) still renders as a list.
+  html = "<ul><li>a<ul><li>b</li></ul></li></ul>"
+  out = convert_html_to_markdown(html, _identity)
+  assert "- a" in out
+  assert "b" in out
+
+def test_max_tree_depth_is_sane():
+  # Cap must be high enough for real documents, low enough to stay under the
+  # interpreter recursion limit with a few frames per level.
+  assert 50 <= _MAX_TREE_DEPTH <= 400
+
+# ── unsafe URL schemes (Finding 5: LOW) ───────────────────────────────────────────
+
+def test_javascript_url_in_link_is_neutralised():
+  # Anchors render their href only in inline context (inside a block like <p>).
+  out = convert_html_to_markdown('<p><a href="javascript:alert(1)">click</a></p>', _identity)
+  assert "javascript:" not in out
+  assert "click" in out  # link text kept, dangerous href dropped
+
+def test_data_and_vbscript_urls_dropped():
+  assert "vbscript:" not in convert_html_to_markdown('<p><a href="vbscript:x">y</a></p>', _identity)
+  assert "data:" not in convert_html_to_markdown('<img src="data:text/html,<script>">', _identity)
+
+def test_normal_urls_pass_through():
+  out = convert_html_to_markdown('<p><a href="https://example.com">site</a></p>', _identity)
+  assert "(https://example.com)" in out
+  img = convert_html_to_markdown('<img src="https://example.com/x.png" alt="pic">', _identity)
+  assert "(https://example.com/x.png)" in img