[FRONTEND] Add real-time task updates with SSE fallback polling

[utksh1]

Problem

SecuScan needs a production-grade improvement in this area: Live scan status UX..

Scope

Introduce a server-sent events endpoint and frontend subscription, with polling fallback and graceful reconnect behavior.

Acceptance Criteria

• The implementation is focused and does not introduce unrelated UI, docs, lockfile, or formatting churn.
• Security-sensitive behavior has explicit negative tests where applicable.
• Existing tests continue to pass, and new tests cover the main success and failure paths.
• Documentation or configuration examples are updated when operator behavior changes.

Verification

Tests should cover SSE events, reconnect, fallback polling, and duplicate event handling.

Difficulty

Hard, useful issue intended for experienced contributors.

[Shikhar-404exe]

Hi ,

I reviewed this issue and the related files. I have experience in this field of work.

I’d like to work on this issue and can start immediately. My plan is to:

reproduce the issue locally
trace the affected components
implement and test the fix carefully

Please add suitable labels and /assign this issue to me under gssoc26 if it's available.
Thank you!