Wallet attribute: Private transfers (beyond stealth addresses)

[polymutex]

The current "Private transfers" attribute should support more privacy-preserving token transfer options than only stealth addresses.

Suggested on the 2025-06-22 call:

• Tornado Cash
• Privacy Pools
• Railgun
• Aztec

We don't have to support all of them for launch, but we should support more than just stealth addresses to reflect the fact that the attribute is credibly about private transfers in general, rather than "picking winners" by appearing to designate stealth addresses as only viable private token transfer tech.