feat: PWA reliability, Advanced Cache & GitHub API Resilience (Phases 1-3)

[saidai-bhuvanesh]

Pull Request: PWA Reliability, Advanced Cache & API Resilience (Phases 1-3)

This PR implements PWA reliability enhancements, advanced caching capabilities, and robust error-recovery mechanisms for the GitHub API integrations.

Phase 1: PWA Reliability & Offline Fallback

• Added a branded offline fallback UI in app/offline/page.tsx (OfflineFallback component).
• Configured the service worker (app/sw.ts) to cache the /offline fallback page during installation.
• Updated the service worker fetch handler to gracefully serve the cached /offline fallback page on navigation failure.
• Implemented corresponding tests in tests/pwa/offline-page.test.tsx.

Phase 2: Advanced Cache Management

• Created versioned cache envelopes (CacheEnvelope) in lib/cache.ts to invalidate structures on schema upgrades.
• Added regex pattern-based cache invalidation (invalidatePattern) to selectively purge cache entries.
• Implemented Stale-While-Revalidate (SWR) logic in DistributedCache to optimize user response speed by returning stale cached data while updating in the background.
• Added comprehensive cache tests in tests/cache-advanced.test.ts.

Phase 3: GitHub API Failure Recovery

• Added jittered exponential backoff retries (getJitteredBackoff) to handle transient rate limits or outages without overloading GitHub.
• Added intelligent error classification (shouldFallbackOnError) to distinguish transient errors from fatal logic/auth exceptions.
• Implemented stale-cache and placeholder mock-data fallbacks in fetchUserProfile, fetchUserRepos, and fetchGitHubContributions.
• Added the isOfflineFallback flag to return data so the UI can notify the user of potentially outdated information.
• Wrote integration tests in tests/github-recovery.test.ts.

[vercel]

Someone is attempting to deploy a commit to the jhasourav07's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

👋 Hey @saidai-bhuvanesh! Thanks for your contribution! 🎉

Unfortunately, this PR has been automatically closed because it is not linked to any open issue.

To resolve this, please do the following:

1. Link a valid open issue by editing your PR description to include a closing keyword (e.g., Fixes #<issue-number>).
2. Reopen this PR once the link is added.

💡 You can link multiple issues if needed (e.g. Fixes #12, Closes #34).
If you're working on something that doesn't have an issue yet, please open one first and then link it here.

We look forward to reviewing your PR once an issue is linked! 🚀