feat: Add report comparison view [Closes #36]

[shravanithouta108]

Description

Adds a new /reports/compare page that lets users select two scan reports and compare them side by side, showing new, fixed, unchanged findings and severity changes between scans.

Related Issues

Closes #36

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?

• Ran 5 unit tests via npm run test — all pass
• Tests cover: new findings, fixed findings, unchanged findings, empty findings edge case, and severity changes
• Manually verified UI on desktop and mobile viewports

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]

Rejecting this as not reviewable for merge. The PR claims to add report comparison, but the diff includes broad unrelated backend, CI, validation, Dockerfile, and test changes, plus an artifact-like file named ; artifact-check and frontend Docker builds are failing. Please open a clean, scoped PR that only implements the report comparison view and its focused tests, without unrelated merged changes or generated artifacts.

[utksh1]

Closed as invalid for this contribution round. The PR is too broad/unrelated to the stated report-comparison feature and currently fails artifact/build checks. Open a clean scoped PR for report comparison only.