Add a copy button to the final report
User currently have to select their submitted code manually to copy it from the final report. Add a Copy code button beside Your final code, preserve the original whitespace and line breaks, and show brief success or error feedback.
Hide the button when code is unavailable, including reports containing the unsaved-code placeholder. Code persistence remains unchanged.
Automated tests cover successful copying, clipboard errors, unavailable code, and repeated clicks while copying.
Closes #318
Summary by cubic
Adds a Copy code button next to "Your final code" in the report so candidates no longer have to select their submission manually. The button copies the original submission text, preserving whitespace and line breaks, and shows "Copied!" feedback or an error message when clipboard access fails.
- Shows a "Copying..." state and a disabled appearance while a copy is pending, and ignores duplicate clicks.
- Hides the button when code is unavailable, including reports with the unsaved-code placeholder. Code persistence is unchanged.