DiscoveryRankingEngine

Deterministic 6-level heuristic ranking engine for discovery preset results.

The ranking order (best-first) is:

1. Highest unique discovered node count

2. Highest neighbor-report diversity (direct + mesh neighbor mentions)

3. Highest non-duplicate packet count

4. Best median link quality (median SNR first, then median RSSI)

5. Greatest best-known distance to a valid-position node

6. Lowest failure / reconnect penalty

If two presets still tie after all heuristics they are labelled as tied.