Refactor and expose initial prompt edit to UI

[adamdbrw]

• It needs to be general, not use-case specific "You are a warehouse layouting expert" is incorrect for general purpose, e.g. for generating orchards, potato fields, etc.
• It can be divided into parts based on probability of the user need to edit, UX-centric. The user will typically not know about prompt engineering but only their goals.
• It needs to utilize automated API generation mechanisms and minimize hand-crafting.
• Think how to handle history.