fix(repo): paginate user repositories in repo explorer

[desireddymohithreddy0925]

Summary

Fixes a bug where the repo-explorer dashboard widget only fetched the first 100 repositories.

Closes #2902, Closes #2903

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Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that changes existing behavior)
• 📝 Documentation update
• ♻️ Refactor / code cleanup (no functional change)
• ⚡ Performance improvement
• 🔒 Security fix
• 🧪 Tests only

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What Changed

• Refactored src/app/api/metrics/repo-explorer/route.ts to utilize the fetchUserRepos utility.
• Paginates via GitHub API to aggregate all repositories regardless of total count instead of only fetching the first 100.

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How to Test

1. Log in with a GitHub account that has more than 100 repositories.
2. Navigate to the Repo Explorer section.
3. Compare the total repository count with GitHub to verify all repositories are now accurately fetched.

Expected result: The application fetches and displays the complete list of repositories accurately.

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Checklist

• Linked the related issue above
• Self-reviewed my own diff
• No unnecessary console.log, debug code, or commented-out blocks
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Added or updated tests where applicable
• Updated documentation / comments if behavior changed

[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

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• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

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• quality:exceptional — ×1.5 multiplier

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[Priyanshu-byte-coder]

The repo-explorer pagination idea is in scope and welcome, but this PR is bundled with the same milestones + goal-category changes as #3135 (ProjectMilestones.tsx, GoalTracker.tsx, add_goal_category migration, goals/route.ts), and the goal-category part already landed via #3194 — so most of this now conflicts and is redundant. Please open a focused PR that changes only src/app/api/metrics/repo-explorer/route.ts + src/lib/github.ts (+ its test) for the pagination, rebased on current main. I'll review that on its own. (Note #2903 attempted the same pagination but failed type-check/build — make sure the new one is green.)