feat: add environment configuration templates

[QUBITABHAY]

This pull request adds example environment variable files for both the backend and frontend, providing clear configuration templates for local development and production. It also updates the frontend .gitignore to more precisely ignore only sensitive local environment files, rather than all .env.* files.

Environment configuration improvements:

• Added backend/.env.example with sample variables for MongoDB, JWT secret, Gemini API key, and server port to guide backend setup.
• Added frontend/.env.example with a sample API URL to guide frontend setup.

.gitignore update:

• Updated frontend/.gitignore to ignore only specific local environment files (.env.local, .env.development.local, .env.test.local, .env.production.local), making it safer to commit example env files and reducing risk of leaking sensitive data.

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[Copilot]

Pull Request Overview

This PR adds environment configuration templates to help developers set up local development environments correctly, while improving security by preventing accidental commits of sensitive environment data.

• Added example environment files for both backend and frontend with sample configuration values
• Updated frontend .gitignore to ignore only local environment files instead of all .env.* files
• Provided clear documentation and guidance for required environment variables

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
frontend/.gitignore	Updated to ignore only local environment files, allowing example files to be committed
frontend/.env.example	Added frontend environment template with API URL configuration
backend/.env.example	Added backend environment template with database, JWT, API key, and port configuration

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