Add CONTRIBUTING.md and GitHub issue/PR templates

[royalpinto007]

Desired outcome

The repo has a CONTRIBUTING.md and GitHub issue and pull request templates.

Why it matters

This repo carries good first issue labelled issues, which invites outside contributors, but there is no .github/ directory at all and no CONTRIBUTING.md at the root. A new contributor has to reverse-engineer everything from package.json: which Node version (engines says >= 20), how to install, that npm run dev is the dev server, that npm run lint exists, that Prettier with prettier-plugin-tailwindcss is configured in .prettierrc.json and must be run before committing, and which env vars from .env.example are needed to boot the app.

The sibling repo SignalizeAI/SignalizeAI already has a CONTRIBUTING.md and a CODE_OF_CONDUCT.md that can be adapted rather than written from scratch.

Steps

1. Add CONTRIBUTING.md covering: prerequisites (Node >= 20), npm install, copying .env.example to .env.local, npm run dev, npm run lint, running Prettier, and the branch and commit conventions.
2. Add .github/ISSUE_TEMPLATE/bug_report.md and feature_request.md, plus .github/PULL_REQUEST_TEMPLATE.md.
3. Link CONTRIBUTING.md from README.md.

Documentation only, no code changes.

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