Add statistics screen design doc

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/plans/2026-02-24-statistics-screen-design.md

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+# Statistics Screen Design
+
+**Date:** 2026-02-24
+**Feature:** Word mastery statistics screen
+**Branch:** feature/statistics-screen
+
+## Summary
+
+Add a statistics screen accessible from the results screen that shows word mastery progress for all vocabulary words. Users can see how well they know each word and reset their statistics.
+
+## Navigation
+
+- Results screen gets a "Statistik anzeigen" button
+- Tapping it switches to the new `Statistics` view state in `Home.razor`
+- A "Zurück zum Start" button returns to the start screen
+- No routing changes required
+
+## Architecture
+
+A new `Statistics` value is added to the existing view state enum in `Home.razor`. Statistics data is read directly from `GameService` (already loaded in memory). A new `ResetStatisticsAsync()` method is added to `GameService` that clears all `CorrectCount`/`IncorrectCount` values and persists to localStorage.
+
+## Statistics Screen Layout
+
+**Header:** Summary line showing total words played and overall accuracy.
+
+**Word list:** Scrollable list of all 20 words, sorted by ascending accuracy (worst first). Words never played appear at the bottom.
+
+Each row contains:
+- Image thumbnail (~80px SVG)
+- Word name (German)
+- Accuracy percentage ("75% richtig") or "—" if never played
+- Progress bar (fills green based on accuracy)
+
+**Footer:**
+- "Zurücksetzen" button (with confirmation) — resets all statistics
+- "Zurück zum Start" button
+
+## Mastery / Progress Bar Logic
+
+- Accuracy = `CorrectCount / (CorrectCount + IncorrectCount)`
+- Never played: shown last, bar at 0%, label "—"
+- Bar color:
+  - Green: ≥ 70% accuracy
+  - Orange: 40–69% accuracy
+  - Red: < 40% accuracy
+
+## Sorting
+
+Words sorted ascending by accuracy so the words needing most practice appear at the top. Never-played words are treated as 0% accuracy but sorted after all played words.
+
+## Reset Flow
+
+Tapping "Zurücksetzen" shows a browser `confirm()` dialog (or inline confirmation). On confirmation, `GameService.ResetStatisticsAsync()` zeros all counts and saves to localStorage. The list refreshes to show all words at 0 / "—".
+
+## Files to Change
+
+- `MemoryGame/Pages/Home.razor` — add Statistics view state and UI
+- `MemoryGame/Services/GameService.cs` — add `ResetStatisticsAsync()` method
+- `MemoryGame/wwwroot/css/app.css` — add statistics screen styles (including tablet breakpoint)