fix: add beautifulsoup4 to requirements.txt for HTML import

Was in pyproject.toml but missing from requirements.txt which the
Dockerfile uses, causing 'No module named bs4' on HTML imports.

Author: GeiserX

requirements.txt

@@ -24,3 +24,5 @@ greenlet>=3.1.0
 pywebpush>=2.0.0
 py-vapid>=1.9.0
 cryptography>=42.0.0
+# HTML import parsing (v7.0+)
+beautifulsoup4>=4.12.0