Function export_html_split 

pub fn export_html_split(
    graph: &KnowledgeGraph,
    communities: &HashMap<usize, Vec<String>>,
    community_labels: &HashMap<usize, String>,
    output_dir: &Path,
) -> Result<PathBuf>

Export a split HTML visualization into output_dir/html/.

Generates:

• html/index.html — overview page where each community is a single super-node, edges represent cross-community connections. Click a community to navigate.
• html/community_N.html — detail page for community N with all its internal nodes and edges. Links back to index and to other communities.

Returns the path to the html/ directory.