Function smart_summary 

pub fn smart_summary(
    graph: &KnowledgeGraph,
    communities: &HashMap<usize, Vec<String>>,
    level: SummaryLevel,
    token_budget: usize,
) -> String

Generate a multi-level graph summary within a token budget.

• Detailed: Equivalent to subgraph_to_text on the full graph.
• Community: One representative node per community (highest degree) + cross-community edges.
• Architecture: Groups nodes by directory into super-nodes, merges edges.