Fix/dashboard polling backoff

[shravanithouta108]

Description

Dashboard.tsx was polling the backend every 10 seconds indefinitely, even when the backend was completely down. This caused unnecessary network requests, stale summary data persisting silently, and no way to recover without a full page reload.

Fixed by adding a healthFailed state flag that stops polling immediately after the first health check failure. The Retry Connection button now resets this flag and restarts polling cleanly instead of reloading the entire page.

Related Issues

Closes #1852

Type of Change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Verified polling stops after backend health check fails
• Verified error state is shown immediately when backend is unreachable
• Verified Retry Connection button restarts polling without full page reload
• Verified normal polling continues as expected when backend is available
• Ran frontend checks: npm run test — all passed

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

[utksh1]

This dashboard polling change is stacked on the unrelated AI-summary, reporting, and Findings edits from #2043. Please rebase onto current main with only Dashboard.tsx plus focused polling/backoff/retry coverage, then rerun checks.

[utksh1]

This branch combines the already-merged Findings layout change with AI summary behavior and Dashboard polling. Please split it into a focused Dashboard polling PR, remove unrelated files, and rebase before re-review.

[shravanithouta108]

Hi @utksh1, addressing your feedback — I found and removed a stray commit that had leaked in an unrelated test_saved_views.py change from a different branch. This PR is now scoped to exactly 2 files: Dashboard.tsx (the polling/backoff/retry fix for #1852) and frontend/package-lock.json (a small postcss dependency bump resolving GHSA-r28c-9q8g-f849, a pre-existing high-severity vulnerability flagged in CI). Let me know if you'd prefer the postcss fix split into its own PR instead — happy to do that if it's cleaner for review. All checks are passing. Thanks for your patience!