docs: document the DHT query 'Type' integer values (closes #1260)

[wrvnnull]

Summary

Closes #1260.

The Type field in the /api/v0/dht/query response was never explained. This adds a table mapping the integer to its go-libp2p routing query event and links to the authoritative definition.

Changes

• docs/reference/kubo/rpc.md: documented Type values 0–3 for /api/v0/dht/query.

Verification

• Values match go-libp2p routing.QueryType.

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