mev_sendBundle privacy.hints default behavior

[This spec](https://docs.flashbots.net/flashbots-mev-share/searchers/understanding-bundles#bundle-definition) doesn't specify the default behavior for privacy.hints. If the `privacy` field is missing, or if `privacy.hints` is missing, what information is shared to the public MEVShare feed? This should be explicit.

Start with the linked Bundle Definition specification and review the surrounding mev_sendBundle privacy documentation. Determine the behavior when privacy or privacy.hints is omitted, then document that default explicitly and verify the wording is consistent with the specification.

Written by the indexing model from the issue text.