feat: enable backend ESLint and Prettier linting in CI

[kush511]

Description

Activates automated ESLint and Prettier linting for the backend, enabling the CI pipeline to enforce code quality standards on every PR and push to main.

Related Issue

Closes #11

How to Test

1. Create a new PR to main branch
2. Check GitHub Actions — backend linting will automatically run
3. Run locally: npm run lint in the backend directory
4. Auto-fix issues: npm run lint:fix

Changes Made

• Installed ESLint, Prettier, @eslint/js, and globals packages
• Created backend/eslint.config.js with Node.js/Express rules and Jest globals
• Created backend/.prettierrc with standardized formatting rules
• Created backend/.prettierignore to exclude build artifacts
• Added npm scripts: lint, lint:fix, format, format:check to backend/package.json
• CI workflow now auto-detects and runs the lint script on every PR

[vercel]

@kush511 is attempting to deploy a commit to the anubhav12302387's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

👋 Thanks for opening a PR, @kush511!

Your PR has entered the 🎯 EventOne GSSoC PR Review Pipeline.

🟢 GSSoC PR detected — your PR will be routed to an approved GSSoC mentor for Stage 2 review.

What happens next

Stage	Reviewer	Checks
Stage 1 — Automated Validation	🤖 Bot	Title format · Issue link · AI Slop · Branch check
Stage 2 — Mentor Review	🧑‍🏫 GSSoC Mentor	Code + Quality Review
Stage 3 — Admin Final Gate	🔑 @anubhavxdev	Label check + Final Merge Decision

A pipeline status comment will appear below and update automatically as your PR progresses.

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While you wait

• Sign all commits using git commit -s
• Link your issue with Closes #123
• Use a feature branch — not main
• Avoid unrelated changes in the same PR
• Write your own description — no AI-generated content

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EventOne × GSSoC Automated Pipeline

[github-actions]

❌ PR Format Check — Failed — Please Fix Below

Hi @kush511! Please fix the issues below before your PR can proceed to mentor review.

❌ Must Fix Before Proceeding

❌ Issue #11 is already closed — You cannot link a PR to a closed issue. Open a new issue for this work.

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📋 EventOne PR Guidelines (click to expand)

Title format — Conventional Commits:
feat: · fix: · docs: · style: · refactor: · test: · chore: · perf:

Always link an issue: Closes #number

Use a feature branch — never PR directly from main

Write your own description — AI-generated content = gssoc:ai-slop label

EventOne × GSSoC Pipeline — Stage 1 Automated Check