Restore the mastery progression worksheet mode that was previously working
but got disconnected during recent development.
Changes:
- Add 'mastery' mode option to ModeSelector (Smart/Manual/Mastery Progression)
- Wire ProgressionModePanel into ConfigPanel's mode selection logic
- Add currentStepId field to WorksheetFormState for tracking progression step
- Mastery mode displays 6-step scaffolding fade progression slider
The mastery progression system uses a 1D slider mapped to a 6-step path
through 3D difficulty space (digit count × regrouping complexity × scaffolding).
Scaffolding cycles back when moving to higher digit counts, following a
pedagogically sound pattern.
Components progressionPath.ts and ProgressionModePanel.tsx already existed
(dated Nov 9) but were not integrated into the UI flow.
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Co-Authored-By: Claude <noreply@anthropic.com>
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