Multi-root BFS & taxpayer totals

1. We filter charities by user-specified EINs + any keywords. EINs are always included, everything else must match at least one keyword unless no keywords are set (then all are included).
2. We pick the BFS root from the largest-receipt_amt EIN (if any exist), otherwise the largest from the filtered set. If that BFS yields fewer than 5 nodes, we pick the next-largest unvisited charity in the filtered set, BFS again, and so on, until the subgraph has 5 or more nodes or we run out.
3. We always include all user-specified EINs plus direct edges among them. Node labels highlight Taxpayer Funds Received from govt_amt, and we sum that for the final subgraph.