Feature/add global ranking

[Yashaswini-K-P]

Description

This PR extends the /api/student/:username endpoint by adding the user's live LeetCode Global Ranking to the API response payload.

Previously, while problem metrics were tracked historically via GitHub repositories, the absolute global leaderboard ranking was not exposed to the student profile layout. This change fetches the most recent global ranking dynamically from the LeetCode API, updates the response body structure gracefully, and implements zero-value fallbacks if the upstream service is unreachable—ensuring complete backward compatibility.

Linked Issue

Fixes #92

Changes Made

• Direct API Upstream Fetching: Configured fetchStudentHistory to initially hit the leetcode-api-dun.vercel.app wrapper to capture the live, un-mutated ranking integer on-demand.
• Resilient Graceful Degradation: Added fallback error handling to default the ranking parameter to 0 or retrieve it sequentially from historical repositories if the upstream wrapper times out or fails.
• Payload Extension: Modified the return utility signature to inject the root-level ranking key directly alongside username and history data to align with frontend consumption criteria.

Type of Change

• Bug fix
• New feature
• UI/Visual update
• Documentation update
• Refactor

Testing

• Tested locally
• Tested on mobile viewport (if applicable)
• No console errors introduced

Checklist

• My code follows the project's coding style
• I have formatted my code locally using Prettier
• I have performed a self-review of my code
• My changes generate no new warnings or errors
• I have updated documentation if required
• I have linked the relevant issue

Screenshots / Screen Recording

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