docs: add .env.example for contributor onboarding

[kumarishreya-ai-ds]

Description

Adds a root .env.example file and improves contributor onboarding documentation.

The repository currently does not require any runtime environment variables. This PR documents that clearly and provides guidance for contributors who may need local overrides in the future.

Related Issue

Closes #1332

Type of Contribution

• Bug fix
• New feature
• Documentation update
• Refactor
• GSSoC contribution

Participant Info

• GitHub username: kumarishreya-ai-ds
• Contribution level (Beginner/Intermediate/Advanced): Beginner

Screen Recording

Recording / Loom link: N/A (Documentation-only change, no UI or feature modifications)

Checklist

• I have read the contribution guidelines
• My changes follow the project structure
• I have tested my changes in Chrome, Firefox, and Safari
• bun run lint passes (documentation-only change)
• bunx tsc --noEmit passes (documentation-only change)
• New interactive elements have aria-label / accessible names
• No console.log statements left in
• This PR is related to a valid issue
• Screen recording attached above (not applicable for documentation-only changes)

Changes Made

• Added .env.example at the repository root
• Documented that the project currently does not require runtime environment variables
• Updated README with environment setup guidance
• Updated CONTRIBUTING.md with onboarding instructions for .env.local

Investigation

Searched the repository for:

• process.env
• import.meta.env
• NEXT_PUBLIC_*
• VERCEL_*

No runtime environment variables are currently used by the project. The new .env.example acts as onboarding documentation and provides a clear starting point for future contributors.

[vercel]

@kumarishreya-ai-ds is attempting to deploy a commit to the magic-peach1's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

✅ PR Format Check Passed — @kumarishreya-ai-ds

Basic format checks passed. A maintainer will review your code changes.

This does not mean the PR is approved — it just means the format is correct.

[github-actions]

👋 Thanks for your PR, @kumarishreya-ai-ds!

Welcome to Reframe — a browser-based video editor built for everyone 🎬

🟠 GSSoC'26 PR detected — thanks for contributing under GirlScript Summer of Code 2026!

What happens next

1. 🤖 Automated checks — build & TypeScript typecheck will run automatically
2. ✅ Vercel preview — a preview deployment will be created (requires maintainer authorization for fork PRs)
3. 👀 Code review — a maintainer will review your changes
4. 🚀 Merge — once approved, your PR will be merged!

Quick checklist

• PR title follows Conventional Commits (e.g. feat: add dark mode)
• Linked the issue this PR closes (e.g. Closes #123)
• Tested the changes locally (bun run dev)
• Build passes (bun run build)

Useful links

• 📖 CONTRIBUTING.md
• 🐛 Open Issues
• ⭐ Star the repo to support the project!

Happy coding! 🎉

[magic-peach]

@kumarishreya-ai-ds please resolve conflicts

[kumarishreya-ai-ds]

@magic-peach can you review now , i have cleared the conflicts?