Stop audio after candidate submission

[floze-the-genius]

Summary

• destroy the active WaveSurfer player after a candidate update succeeds
• do the teardown before reloading the detection list removes the player's card
• leave playback untouched when the update request fails

Fixes #592.

Validation

• dotnet restore -r win-x86
• dotnet build --no-restore -c Release -r win-x86 (0 errors; existing net6/toolchain warnings remain)
• dotnet test --no-restore -r win-x86 (completed successfully; the solution has no test projects)
• dotnet publish --no-restore -c Release -r win-x86 -o /tmp/orcahello-592-publish
• targeted submit-order assertion: origin/main fails the required successful-update → player-teardown → list-reload sequence; this patch passes it

AI assistance

Codex (GPT-5) identified the missing lifecycle call, applied the one-line patch, and ran the validation above.

[kauereinbold]

This is a first contribution from someone new to the project, and we haven't set how we handle reviews for contributors who haven't been involved before. @dthaler, can we discuss how you want to handle first-time contributions before this one gets approved? I'm testing the change locally in the meantime and will post findings separately.

[dthaler]

how you want to handle first-time contributions

First-time contributions are welcomed and gratefully accepted.
As long as it's tested and code reviewed by someone else, and solves a real problem, contributions are good to go.

[kauereinbold]

Tested locally and it is working.