fix: cache repository languages fetch

[Sammmyyyyyyy]

Summary

Adds repository-level caching for GitHub language statistics to reduce unnecessary API calls and improve dashboard performance.

Closes #967

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

Changes Made

• Added languages cache TTL entry with a 6-hour duration
• Added per-repository caching for GitHub /languages API requests
• Added repo-specific cache keys using repoName
• Removed redundant outer cache wrapper to avoid nested cache inefficiencies
• Preserved cache bypass behavior for manual refresh actions

How to Test

Steps for the reviewer to verify this works:

1. Run the development server using npm run dev
2. Open the dashboard and load the language breakdown widget
3. Verify repository language requests are cached
4. Trigger a manual refresh and verify fresh GitHub API data is fetched
5. Confirm no TypeScript or runtime errors occur

Screenshots (if UI change)

N/A

Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

[vercel]

@Sammmyyyyyyy is attempting to deploy a commit to the PRIYANSHU DOSHI's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

GSSoC Label Checklist 🏷️

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