fix : validate username format in contributions route

[tmdeveloper007]

Summary of What Needs to be Done:
The contributions route at src/app/api/metrics/contributions/route.ts uses username parameter in GitHub API queries without validating it contains only valid GitHub username characters.

Changes that Need to be Made:

• File: src/app/api/metrics/contributions/route.ts (line 103)
• Add regex validation for username format: ^[a-zA-Z0-9-_]+$

Impact that it would Provide:

• Prevents invalid API requests
• Makes the code more robust against malformed input

[github-actions]

✅ Closed as completed!

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