chore: enable All Contributors bot and add myself as contributor

[SUJALGOYALL]

PR: Enable All Contributors Bot and Add Initial Contributor

Description

This pull request enables the All Contributors bot for the MailMERN project and adds the initial contributor (@sujalgoyall).

• Initializes .all-contributorsrc with the project configuration
• Adds the contributors section and badge to README.md
• Sets up the repository to allow future contributors to be automatically added via the bot

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Semver Changes

• Patch (bug fix, no new features)
• Minor (new features, no breaking changes)
• Major (breaking changes)

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Issues

Closes #18

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How Contributors Can Add Themselves

Once this PR is merged, future contributors can be added in two ways:

1. Via GitHub comment:
   Comment on a PR or Issue:
   @all-contributors please add @username for code, doc
   The bot will automatically create a PR to update the README.

2. Via CLI on a fork:
   Contributors can run:

   npx all-contributors add <their-github-username> <types>

   Then submit a PR from their fork. Once merged, the README will update automatically.

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Checklist

• I have read the Contributing Guidelines
• I have added myself as an initial contributor
• The README now includes the contributors section and badge

[MD-IRFAN-RAJ]

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