Better local dev/testing environment

[owencooke]

During development, it would be better to avoid making too many LLM calls when testing features and avoid adding data to the prod DB. These are just a few potential concerns, others would be test emails, etc

• Local Postgres DB for testing via Docker
• A way to test/mock GitHub integration, without creating repo each time
• Mocked LLM calls
• Mock emails

[owencooke]

Note: i've started this for LLMs by adding MOCK_LLM env varable. but i'm currently using it to shortcut out of server methods, could be better to mock the actual LLM calls themselves at a lower level, to test more logic behaviour in route methods