fix: allow repeating a resolved exercise in a semi-structured session

[ErickMascarenhas]

Summary

• Allowed picking an exercise that already has a result again during a semi-structured session, whether it was completed, deferred or not performed
• Recorded each repeat as its own execution instead of overwriting the previous one
• Kept the list locked only while another exercise is actually running
• Kept the result icon on a resolved exercise and added the chevron back, so it still reads as something that can be run again

Validation:

• Local tests on mobile
• Checked diffs locally