As a client I want to be able to initiate a deployment once I've approved all changes on a branch

When all tickets associated with a particular Git branch are marked as approved, controls appear on the screen for the client to deploy it.

When they choose to deploy, instructions are sent to the deployment system to either (a) deploy to staging, (b) deploy to production, or (c) deploy to staging and production. We'll probably pick one and hardcode it for starters, with the final decision dependent on other tickets.

When a deployment is initiated, the screen updates dynamically with a rough indication of progress and ultimate/success failure, and any other information the client needs to see.

Behind the scenes, the code will run a Git merge, then contact the deployment API to deploy it.