DOCS UPDATE: Improve InPactAI Backend Setup Instructions + Add Setup Walkthrough Video

### Is this related to an existing part of the documentation?

- [x] Yes, it is related to an existing section

### What needs to be updated?

## Current Documentation Issue
While setting up InPactAI for local development, I ran into a few issues, especially those involving backend setup, that I believe many new contributors might also face, these include incorrect setup guide in `README.md` for backend `.env` file placement, folder navigation, and a few more.

## Proposed Changes
1. Update the `README.md` to include:
- Clear instructions on when to navigate into which directory.
- Proper clarification on where `.env` files should be created.
- Notes for troubleshooting (possibly giving [link to the discord server](https://discord.com/channels/1022871757289422898/1345044736515379210) to seek help)

2. Add a short setup video (screen recording) that walks through:
- Project setup.
- Supabase project creation + credential extraction.
- How to start the server (both frontend and backend)

## Additional Context:

Incorrect guidance in `README.md`⬇️

### Relevant Documentation Link (if any)

https://github.com/AOSSIE-Org/InPactAI/blob/main/README.md

### Record

- [x] I agree to follow this project's Code of Conduct
- [x] I want to work on this update