Add PWA support with offline capability and install prompt

[Kingsman-99]

Overview

Add Progressive Web App support so users can install StellarSplit on mobile and desktop and browse cached invoice data offline.

Acceptance Criteria

• manifest.json with app name, icons (192px, 512px), theme color, and display: standalone
• Service worker registered via next-pwa caching static assets and recent API responses
• Offline fallback page shown when network is unavailable
• "Install App" banner shown on supported browsers after 30 seconds of use
• Install prompt dismissible and suppressed for 7 days after dismiss
• Lighthouse PWA audit score: 100

[quartune]

@quartune has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Maintainer,

I am interested in this issue and believe I can deliver a high-quality solution

ℹ️ Repo Maintainers: To accept this application, review their application or assign @quartune to this issue.

[CyberXpert607]

@CyberXpert607 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hey team,

I'll take #321.

I'll add full PWA support: manifest.json with icons, next-pwa service worker caching static assets and recent API responses, offline fallback page, and an install banner that appears after 30 seconds (dismissible, suppressed for 7 days). Targeting a 100 Lighthouse PWA score.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @CyberXpert607 to this issue.

[okechukwuchisomjoy-cloud]

@okechukwuchisomjoy-cloud has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Please assign this issue to me. I can handle it professionally.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @okechukwuchisomjoy-cloud to this issue.

[grantfox-oss]

🦊 GrantFox — @quartune has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #321)
2. Your PR will be reviewed by the Stellar-split maintainers

Good luck! Track your progress on GrantFox.

[drips-wave]

Congratulations, @quartune! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @quartune: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@quartune's PR #341 was approved and merged by @Kingsman-99.

🏆 @quartune: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (83 total points). Track your full progress on GrantFox.

👏 Great work, @quartune! Keep contributing to Stellar-split.

[drips-wave]

This issue has been completed by @quartune as part of the Stellar Wave Program's 6th Wave 🥳

😎 @quartune: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.