[verified] test: guard index.html against merge junk

Refs #1336
Refs #1338

- assert index.html has no conflict markers or stray markdown
- assert cleaned single-instance blocks stay single

tests/test_index_html_integrity.py

@@ -0,0 +1,10 @@
+from pathlib import Path
+
+
+def test_index_html_integrity():
+    text = (Path(__file__).resolve().parents[1] / 'index.html').read_text(encoding='utf-8')
+    for marker in ('<<<<<<<', '=======', '>>>>>>>', '```html', '⚠<EFBFBD>'):
+        assert marker not in text
+    assert 'index.html\n```html' not in text
+    for needle in ('View Contribution Policy', 'id="mem-palace-container"', 'id="mempalace-results"', 'id="memory-filter"', 'id="memory-feed"', 'id="memory-inspect-panel"', 'id="memory-connections-panel"'):
+        assert text.count(needle) == 1