[Design] Create user journey for mentioning people

[setch-l]

Users can mention people in multiple ways in the app. Let's create user journey's for all the different options:

• typing @ which opens a search query
• pasting an npub
• typing in a NIP05
• pasting a NIP05

Notes from our discussion w/ Martin: https://docs.google.com/document/d/1rKxVvdXiFxVo2m97AwgfkJEuCsmyLgVefvDYaLYT36k/edit