feat(ui): remove mobile bottom nav on phones

Closes #425:

tests/test_issue_code_syntax_highlight.py

@@ -0,0 +1,25 @@
+"""Regression tests for fenced code block syntax highlighting."""
+from pathlib import Path
+
+UI_JS = Path(__file__).resolve().parent.parent / "static" / "ui.js"
+
+
+def _read_ui_js() -> str:
+    return UI_JS.read_text()
+
+
+def test_fenced_code_blocks_add_prism_language_class():
+    js = _read_ui_js()
+    assert 'class="language-${esc(normalizedLang)}"' in js, (
+        "Fenced code blocks should add Prism language-* classes so syntax highlighting works"
+    )
+
+
+def test_fenced_code_blocks_keep_existing_pre_header_layout():
+    js = _read_ui_js()
+    assert 'return `${h}<pre><code${langAttr}>${esc(code.replace(/\\n$/,' in js, (
+        "The syntax-highlight fix should preserve the existing fenced code block layout"
+    )
+    assert '<div class="code-block">' not in js, (
+        "This fix should not introduce a new wrapper around fenced code blocks"
+    )