Add Nakamoto Mainnet Modal Announcement

[elenananana]

Describe the solution you'd like
Add Nakamoto 3.0 Modal for Naka activation. It should be up for a week.

Additional context
Copy:

Nakamoto Activation

Nakamoto 3.0 is live on Stacks Mainnet

[Image]

• Button Copy: Experience Fast Blocks and Bitcoin Finality

• Button Link: Takes you to the Explorer

• Secondary Copy: Learn more about Nakamoto on Mainnet

• Secondary Copy Link: Stacks Foundation Announcement

[BLuEScioN]

@elenananana Shouldn't mainnet be the selected dropdown item in the image/ui?

[andresgalante]

Nick, the image is not ready yet, Ginny will have it tomorrow

[ginny-d]

@BLuEScioN Please use this image:

Mock up: