docs: add CONTRIBUTING guide, PR template, and issue templates

[JemimahEkong]

Description

This PR adds essential contributor documentation to improve onboarding and contribution quality across the repository.

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What’s Included

• Added CONTRIBUTING.md with:

  • Development setup (backend, client, database)
  • Environment variable guidance
  • Branch naming and commit conventions
  • PR guidelines and code review standards

• Added PR template:

  • Standardizes pull request structure and review expectations

• Added issue templates:

  • Bug report template
  • Feature request template

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Why This Matters

New contributors previously lacked clear guidance on how to:

• Set up the project locally
• Structure contributions
• Follow consistent coding and PR standards

These additions reduce friction, improve code quality, and make collaboration more efficient.

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Test Plan

• Verified all commands in CONTRIBUTING.md align with project scripts
• Confirmed templates render correctly in GitHub UI
• Ensured documentation is clear and actionable for new contributors

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Related Issue

Closes #190

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Checklist

• Documentation is clear and complete
• Commands reflect actual project setup
• No unrelated changes included

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