UI: Create app landing page

[sbland]

The app home page (logged in) needs implementing.

Can be based on outline in Miro board once signed off by team: https://miro.com/app/board/uXjVLA_OTE0=/?moveToWidget=3458764617506249899&cot=14

• Signed off and ready to implement

Current state

Not implemented

Target State

Pre-requisite Tasks

• Add registration/login.html to main/templates/registration/ #128
• Authentication implementation

Tasks

• Remove unused placeholder UI elements
• Add text

[connoraird]

PR raised here #274