Improve New Contributor Onboarding and Local Setup

[Saurabhtbj1201]

Title

docs: improve onboarding and setup instructions for first-time contributors

Description

We are opening MindSpace for open-source contributions and need a smoother onboarding flow for new contributors.

Current setup information is partially available, but contributors still need clearer guidance for:

• Backend setup and run commands
• Frontend local serving
• Environment variable expectations
• Common troubleshooting tips

Proposed Tasks

• Add a dedicated docs/SETUP.md with step-by-step setup for Windows, macOS, and Linux
• Add .env.example files where missing (without secrets)
• Add a troubleshooting section for common errors (port conflicts, missing dependencies)
• Cross-link docs from README.md and CONTRIBUTING.md

Acceptance Criteria

• A new contributor can run backend and frontend locally in under 20 minutes
• Setup docs include platform-specific commands
• No secrets are exposed in examples

Labels

documentation, good first issue, help wanted

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