fix(AI): use openai SDK directly + schema

[mikewuu]

OpenAI now supports structured JSON output with 100% accuracy. Which means we don't need langchain anymore:

https://openai.com/index/introducing-structured-outputs-in-the-api/

• [ ] use openai sdk + zod typings
• [ ] remove langchain packages

[mikewuu]

Backlogging until open ai sdk is better. see #199

[homie-dev-mike[bot]]

Here are some pull requests that might be helpful reference for this task:

• fix(Task/Duplicate): failing to check duplicate
• feat(Task): calculate estimates