[BE-71] Restore the deleted root .gitignore

[yusuftomilola]

Overview

The repository has no .gitignore at the root. It was removed in commit f28e3f8 along with backend/.env.example and backend/.eslintrc.js.

Without it, node_modules/, dist/, .env, target/, and editor files are all untracked-but-unignored — the next contributor who runs git add -A will commit thousands of dependency files, or worse, a real .env containing database credentials.

Tasks

• Restore a root .gitignore covering: node_modules/, dist/, build/, .next/, coverage/, contracts/target/, *.log, .DS_Store, and editor directories.
• Ignore all env files (.env, .env.local, .env.*.local) while keeping .env.example tracked.
• The previous version is recoverable — git show f28e3f8^:.gitignore — use it as the starting point.
• Verify with git status on a clean install that no dependency or build output appears as untracked.
• Confirm nothing sensitive was already committed: git log --all --diff-filter=A -- '*.env'.

Acceptance Criteria

• A root .gitignore exists and covers all three workspaces (backend, frontend, contracts).
• npm install in both backend/ and frontend/ leaves git status clean.
• .env.example remains tracked; real env files are ignored.

Notes for Contributors

The backend is being rebuilt from a clean NestJS skeleton — backend/src/ currently contains only app.module.ts, app.controller.ts, app.service.ts, and main.ts. Follow standard NestJS module structure (module / controller / service / dto / entities) and register your module in app.module.ts. Comment below to be assigned.