Add safe_html() for XSS-safe WYSIWYG HTML sanitization

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Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -29,6 +29,7 @@
         "concat-with-sourcemaps": "^1.1.0",
         "cross-env": "^7.0.3",
         "decomment": "^0.9.5",
+        "dompurify": "^3.3.1",
         "easymde": "^2.20.0",
         "esbuild": "^0.25.9",
         "jquery": "^3.7.1",