fix: confirm F2 resets before discarding learner edits

[abhiksark]

Motivation

F2 currently resets learner code immediately. Reset is destructive from a learner perspective, so the default TUI path must make cancellation easy and failures visible.

Current evidence

• The documented interface maps F2 to reset the current exercise.
• Reset snapshots live under .pythonlings/originals/, and reset failures are possible when a snapshot is missing or unreadable.
• The TUI suite already uses Textual pilot tests for interactive behaviour.

Exact scope

Add a safe-default confirmation modal for F2 reset. y confirms; n and Esc cancel. Reset errors must render visibly in the TUI instead of propagating as a crash.

Acceptance checklist

• Pressing F2 opens a confirmation modal before any learner file is changed.
• y performs the reset and refreshes the current exercise view.
• n and Esc cancel without changing the learner file or progress state.
• Missing/broken reset snapshots show an actionable visible error and leave the TUI running.
• Focus and key handling remain predictable while the modal is open.
• Textual pilot tests cover confirm, cancel via n, cancel via Esc, and visible reset failure.

Explicit exclusions

Do not change CLI pythonlings reset confirmation semantics, add a bulk-reset flow, auto-save destructive changes, or redesign unrelated TUI navigation.

Likely files

• pythonlings/screens/track.py and/or pythonlings/app.py
• pythonlings/widgets/ or pythonlings/screens/ modal component (new as needed)
• pythonlings/pythonlings.tcss
• tests/tui/test_app_pilot.py

Verification

python -m pytest tests/tui -q
python -m pytest -q

Manually run the TUI against a fixture workspace and exercise confirm, both cancel keys, and a deliberately missing snapshot.

Sprint coordination

See the sprint Discussion. This issue is unassigned and is not a reservation.

[coderabbitai]

🔗 Related PRs

#31 - feat: overall progress, completion celebration, first-launch welcome (#14, #15, #16) [merged]

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