Add JWT authentication for secure sessions

[rohan911438]

Replace basic verification flow with JWT-based authentication for better security.

Changes:

Generate JWT after login
Store securely (httpOnly cookies or secure storage)
Add token validation middleware

[Junman140]

@Junman140 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

hello i would love to work on this please

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Junman140 to this issue.

[drips-wave]

Congratulations, @Junman140! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @Junman140: 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.

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🌊 Happy Wave 🌊

[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @Junman140 as part of the Stellar Wave Program's 4th Wave 🥳

Moderator's reason: [Auto-assessed] The PR has been open for more than 24 hours with no maintainer objections. It provides a comprehensive implementation of JWT-based authentication including middleware, session management, and route protection as requested in the issue.

😎 @Junman140: 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.

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

ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.