Add purple reset button and restore imported testcase inputs/outputs

[mohamedhabibabid]

Summary

Add a new purple Reset button in the judge workspace that restores the current
cases to the original imported test set.

Motivation

During Codeforces rounds, I frequently need to reset the testcase environment.
It is common to edit input/output fields directly, and sometimes I modify tests
accidentally without realizing it. This makes a one-click restore back to the
original imported tests very useful.

What changed

• Stored a copy of the original imported testcase set when a problem loads.
• Added a new Reset button to the judge action toolbar.
• Reset restores testcases input/output fields back to the original imported data from problem statements.
• Updated CaseView so testcase textareas re-sync correctly when cases are
  replaced.
• Styled the reset button with a purple theme.

Validation

• Built successfully with npm run webpack-production.
• Verified that reset restores the original imported testcase fields.

Notes

This feature improves contest workflow by making it easy to recover from
accidental testcase edits and keep the sample test environment consistent.