feat: add PWA offline dashboard support

[Kishalll]

Summary

Adds PWA offline support so the dashboard can load with cached data when the app is offline.

Closes #1050

Type of Change

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

Changes Made

• Added next-pwa and configured runtime caching in next.config.mjs.
• Added network-first caching for dashboard/API routes, GitHub API responses, and goals/streak/metrics
  data.
• Added cache-first handling for static assets and fonts with 24-hour cache expiry.
• Added a global OfflineBanner that shows Offline — showing cached data.
• Added a custom service worker layer to refresh dashboard caches when the connection returns.
• Added safe offline JSON fallbacks for uncached API requests so widgets do not stay stuck in skeleton
  loading.
• Added background sync queueing for POST /api/goals/sync.
• Regenerated production service worker assets.

How to Test

1. Run npm run build.
2. Run npm run start.
3. Open http://localhost:3000/dashboard with internet enabled.
4. Wait for dashboard widgets to finish loading.
5. Confirm /sw.js is registered in browser DevTools under Application/Service Workers.
6. Turn off internet or enable offline mode in DevTools.
7. Reload /dashboard.
8. Verify the dashboard loads with cached/fallback data and shows the offline banner.

Screenshots (if UI change)

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

Validation completed: npm run build passes.

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[github-actions]

GSSoC Label Checklist 🏷️

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

Difficulty (pick one):

• 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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Points formula: (difficulty × quality_multiplier) + type_bonus

[Kishalll]

@Priyanshu-byte-coder completed both the prs assigned to me , ready to work on other issues

[Priyanshu-byte-coder]

CI is failing on this PR. Please fix the failing checks before this can be merged.

[Kishalll]

@Priyanshu-byte-coder fixed ci issues and the pr is not clean

[Priyanshu-byte-coder]

Thanks for working on PWA offline support! However, there are significant issues with this implementation:

1. Committed pre-built service worker files — public/sw.js, public/workbox-07cb5bfa.js, public/fallback-Gl9L3J2PvQllaLGPIoSXH.js, and public/worker-Gl9L3J2PvQllaLGPIoSXH.js are build artifacts with content-hashed filenames. These should be gitignored and generated at build time — committing them means they'll go stale after the next build.

2. next.config.mjs changes — 127+ line diff to a critical config file needs careful review. Please explain what each change does.

3. worker/index.js — 233 lines of service worker logic. Is this the source for the build artifacts in public/? If so, the build step should generate the public files from this source.

Recommended approach:

• Add the generated service worker files to .gitignore
• Add a build step that generates them from source
• Keep next.config.mjs changes minimal

Please rework the implementation to not commit build artifacts to the repo.

[Priyanshu-byte-coder]

Two issues:

1. The PR commits built artifacts directly: public/sw.js, public/workbox-07cb5bfa.js, public/fallback-*.js, public/worker-*.js. Generated files should not be committed to the repo.
2. The next.config.mjs change conflicts with current main.

Please remove the built PWA artifacts from the commit and rebase onto current main. The next-pwa integration is otherwise a good addition.

[Kishalll]

@Priyanshu-byte-coder will do a pr fixing this shortly

[Priyanshu-byte-coder]

This PR includes compiled PWA build artifacts (public/sw.js, public/workbox-*.js, etc.) that should not be committed to the repository — these are generated at build time. Please add these to .gitignore and remove them from the PR. Also rebase on main to resolve the existing conflicts.

[Kishalll]

@Priyanshu-byte-coder Updated PR based on the review comments and resolved conflicts.

• Removed committed generated PWA artifacts from the PR.
• Added generated PWA files to .gitignore.
• Removed the orphan worker/index.js.
• Kept the next-pwa integration so public/sw.js is generated at build time instead of committed.
• Resolved the package-lock.json and src/app/layout.tsx conflicts.

[Priyanshu-byte-coder]

PR still includes compiled PWA build artifacts: public/sw.js, public/workbox-*.js. These are generated at build time and must not be committed. Add them to .gitignore and remove them from the PR, then rebase on main.

[Kishalll]

@Priyanshu-byte-coder sorry for all the confusions earlier, i commited new changes along w old ones without force pushing that caused a lot of issue and i hv cleaned those noe,
pls review

[Priyanshu-byte-coder]

PWA offline support merged into main (commit f27c710). Thank you @Kishalll!

[Kishalll]

@Priyanshu-byte-coder the mergre conflicts needs to resolved before merge ryt ??to work properly, i was working on this now.