Add parent/teacher progress dashboard

[JesseRWeigel]

Summary

Add a progress dashboard view for parents and teachers to review a student's learning analytics. This helps identify strengths, weaknesses, and learning patterns. Inspired by Alpha School's data-driven approach to identifying and addressing learning gaps.

⚠️ NEEDS DISCUSSION: This feature needs maintainer input on scope, privacy considerations, and whether data should remain local-only or support any form of sharing/export. Please comment with preferences before starting work.

Implementation Details

• Access: Separate view accessible via a settings menu option or a URL parameter (e.g., ?view=dashboard). Consider a simple PIN or toggle to prevent kids from accidentally entering it.
• Analytics charts:
  • Accuracy over time per operation: Line chart showing accuracy % trends for addition, subtraction, multiplication, division
  • Time spent per session: Bar chart showing daily/weekly practice time
  • Problems solved per day: Bar chart showing daily problem count
  • Speed trends: Average time-to-answer over time
• Weakness identification: Highlight the weakest operation/difficulty combination and suggest targeted practice (e.g., "Needs more practice with Hard Division").
• Data export: Export all progress data as CSV for use in spreadsheets or school systems.
• Data source: All data comes from localStorage — the same data tracked by the game.
• Charting: Use a lightweight charting library (e.g., Chart.js or Recharts since the project uses React).

Acceptance Criteria

• Dashboard view is accessible from settings or URL parameter
• Accuracy over time chart renders per operation
• Time spent per session chart renders
• Problems solved per day chart renders
• Weakest area is identified and highlighted with a recommendation
• Data can be exported as CSV
• Dashboard reads from existing localStorage game data
• Dashboard is read-only (cannot modify game progress)

Notes

• This issue is marked as needing discussion. Privacy and scope need to be decided before implementation.
• All data is currently local-only (localStorage). This keeps things simple and private but means data doesn't sync across devices.
• Consider what happens when localStorage is cleared — the dashboard should handle empty/missing data gracefully.
• The dashboard should be responsive but is primarily a desktop/tablet feature.
• Future enhancement: optional cloud sync for multi-device families (out of scope for this issue).