feat: implement scheduled recurring scans with blackout windows (#253)

[YerraguntaAjayKumar]

Description

Implemented a cron-like scheduling service to automate recurring scans. This includes a robust croniter-based parser with zoneinfo timezone handling, an interceptor to evaluate blackout windows (including overnight shifts), and a conservative missed-run recovery policy to safely handle system downtime. Additionally, built a responsive React UI (ScanScheduleForm) with strict client-side validation enforcing 5-part cron syntax.

Related Issues

Fixes #253

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Executed the backend test suite (./testing/test_scheduler.py), verifying all 19 tests pass for timezone boundaries, blackout skips, missed-run recovery, and disabled schedules.
• Added 40+ frontend unit tests in ScanScheduleForm.test.jsx.
• Manually verified UI rendering locally and tested strict validation rejections on malformed inputs (invalid cron strings, mismatched blackout windows).

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.

[YerraguntaAjayKumar]

Hi @utksh1, the implementation is complete and all CI/CD checks are green! It is ready for your review whenever you have a moment. Let me know if you'd like any adjustments to the blackout window logic or the frontend React components

[utksh1]

Thanks for the work here. I cannot merge this in its current shape because the feature is mostly standalone and not integrated into the existing SecuScan scheduling flow.

Required changes:

• Wire the scheduling model/API/UI into the existing scan/workflow creation path so users can actually create, list, update, and execute recurring scans from the app.
• Convert the frontend work to the repo conventions (.tsx, existing styling/layout patterns, existing test location/naming). The current new JSX/CSS module component sits outside the current UI system and is not reachable.
• Avoid adding a parallel scheduler utility that duplicates existing scheduler/workflow behavior unless it is explicitly integrated with the production scheduler.
• Make the missed-run recovery logic deterministic/testable; the current tests mostly assert return types because the code calls wall-clock datetime.now() directly.

Once this is wired into the real product path and covered with meaningful integration tests, I can re-review.