Mobile nav becomes a hamburger menu; Juniper joins the Help page

The horizontally scrolling nav strip lost its scroll position on every
page load and hid the far entries. The top bar is now brand +
hamburger (aria-expanded/aria-controls, 44px target); the nav drops
down as the same stacked list the desktop rail shows — badges, gold
current-page marker — and navigation naturally closes it.

Help gains "The piper": Juniper's full artwork with credit and the
trademark attribution, which mobile previously never showed anywhere
(the sidebar portrait is hidden there). Also fixes the Help cards
flex-rowing their paragraphs into accidental columns on desktop —
visible in the README's own screenshot — via a card.prose block
variant.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jXZFSTZQKzAC8fqpWSz9g

tests/test_web_dashboard.py

@@ -205,7 +205,7 @@ def test_both_pages_carry_navigation_and_skip_link(tmp_path):
     web = _app(_cfg(tmp_path))
     for path, current in (("/", 'href="/"'), ("/review", 'href="/review"')):
         html = web.get(path).text
-        assert 'nav aria-label="Primary"' in html
+        assert 'aria-label="Primary"' in html
         assert f'<a {current} aria-current="page"' in html.replace("\n", " ") or (
             current in html and 'aria-current="page"' in html
         )
@@ -232,7 +232,7 @@ def test_every_page_serves_with_shared_shell(tmp_path):
     ):
         html = web.get(path).text
         assert marker in html, path
-        assert 'nav aria-label="Primary"' in html, path
+        assert 'aria-label="Primary"' in html, path
         assert 'aria-current="page"' in html, path
         assert "logo-full.jpg" in html, path  # Juniper's portrait in the rail
         assert "art by Juniper" in html, path