Add Support for Privy

[jbowen93]

• They’re adding cosmos support in ~1 mo
• They support Coinbase Pay and MoonPay for fiat onramp
• We should be able to generate both a cosmos address and an EVM address from the same login (email or w/e). This is important because people will need to fiat onramp either TIA to Celestia or USDC to Noble, they can’t withdraw from Coinbase direct to flame. But this should allow a clean “send to self” flow.
• They use Shamir secret sharing for key splitting. Privy is “Scott approved” on security.
• They have an option for an “ecosystem wallet” where we can essentially act as a channel partner and allow any future apps on Flame EVM to use the same embedded wallet created through our frontend.
• Recommended example app to look at is Vector (https://www.vector.fun/) which they support.

From Privy:

These docs below are a great start! Let me wrap everything into one message so it's clean.

1. You can create a Privy account here!

2. Our demo and API docs will be really helpful to review as you integrate / play around with Privy

3. Here's the Quickstart guide! Check out our native account funding docs as well

4. Here's our RN Expo SDK guide! Whenever you're ready to move on native mobile, you'll have the same underlying user account with this

5. As mentioned in DMs, we'd recommend deriving Cosmos addresses and setting it as custom metadata! That way, you'll always have it as part of the user object.