Add GitHub Copilot instructions for contribution workflow

[Copilot]

Adds .github/copilot-instructions.md to provide context-aware guidance for contributors using GitHub Copilot.

Key Sections

• Commit format requirements - Emphasizes mandatory gitmoji + type + scope + subject format with examples:

  :sparkles: feat(like-service): Add endpoint for like count retrieval
  :bug: fix(user-auth-service): Fix JWT token validation error
  :memo: docs: Update installation instructions in README
  

• Commitlint validation - Documents all 12 valid commit types (feat, fix, refactor, docs, test, perf, revert, style, build, ci, wip, chore) with descriptions matching CONTRIBUTING.md

• Documentation index - Links to CONTRIBUTING.md, DEV-GUIDE.md, FAQ.md for deeper reference

• Architecture context - Lists all 10 microservices with languages and purposes to help scope changes correctly

• Development workflow - Covers local Kubernetes setup with skaffold, testing, and cleanup commands

• Security note - Flags that vulnerabilities are intentional to prevent well-meaning but incorrect fixes

Maintains consistency with existing documentation while providing actionable guidance for AI-assisted development.

Original prompt

Add instructions for copilot on how to contribute. Make sure to emphasize the commitlint rules as well as what is relevant in the docs.

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