feat: add sound effects, improved stroke recognition, instant locale switching with scramble text animation

- Add SoundManager with Web Audio API synthesized sounds (stroke error, drawing complete, session complete)
- Add sound effects toggle in settings (persisted via localStorage)
- Improve stroke recognition: curvature similarity, max point deviation, stroke length ratio checks
- Loosen thresholds for long strokes and first-stroke positioning
- Implement instant locale switching (no save required)
- Add ScrambleText component with character-by-character morphing animation
- Apply ScrambleText globally across all views, widgets, and dialogs
- Add i18n keys for sound effects settings (EN/DE/JA)

client/src/plugins/i18n.js

@@ -44,8 +44,13 @@ const messages = {
       learned: "You've learned {n} new kanji.",
       components: 'Components',
       observe: 'Observe Stroke Order',
+      replay: 'Replay',
       trace: 'Trace',
       drawStep: 'Draw ({n}/{total})',
+      sectionMeaning: 'Meaning',
+      sectionMnemonic: 'Memory Aid',
+      sectionReadings: 'Readings',
+      learnedKanji: 'Kanji Learned',
       backToDashboard: 'Back to Dashboard',
     },
     hero: {
@@ -70,6 +75,7 @@ const messages = {
       next24: 'Next 24h',
       availableNow: 'Available Now',
       inHours: 'In {n} hour | In {n} hours',
+      inDays: 'In {n} day | In {n} days',
       noIncoming: 'No reviews incoming for 24 hours.',
       items: 'items',
       reviewsCount: '{count} reviews',
@@ -96,6 +102,9 @@ const messages = {
       strict: 'Strict',
       loose: 'Loose',
       save: 'Save & Close',
+      soundEffects: 'Sound Effects',
+      on: 'On',
+      off: 'Off',
     },
     review: {
       meaning: 'Meaning',
@@ -109,6 +118,9 @@ const messages = {
       next: 'NEXT',
       sessionComplete: 'Session Complete!',
       levelup: 'You leveled up your Kanji skills.',
+      levelsUp: '{n} leveled up',
+      levelsDown: '{n} leveled down',
+      results: 'Results',
       back: 'Back to Collection',
       caughtUp: 'All Caught Up!',
       noReviews: 'No reviews available right now.',
@@ -174,8 +186,13 @@ const messages = {
       learned: 'Du hast {n} neue Kanji gelernt.',
       components: 'Komponenten',
       observe: 'Strichfolge beobachten',
+      replay: 'Wiederholen',
       trace: 'Nachzeichnen',
       drawStep: 'Zeichnen ({n}/{total})',
+      sectionMeaning: 'Bedeutung',
+      sectionMnemonic: 'Merkhilfe',
+      sectionReadings: 'Lesungen',
+      learnedKanji: 'Gelernte Kanji',
       backToDashboard: 'Zurück zur Übersicht',
     },
     hero: {
@@ -200,6 +217,7 @@ const messages = {
       next24: 'Nächste 24h',
       availableNow: 'Jetzt verfügbar',
       inHours: 'In {n} Stunde | In {n} Stunden',
+      inDays: 'In {n} Tag | In {n} Tagen',
       noIncoming: 'Keine Reviews in den nächsten 24h.',
       items: 'Einträge',
       reviewsCount: '{count} Reviews',
@@ -226,6 +244,9 @@ const messages = {
       strict: 'Strikt',
       loose: 'Locker',
       save: 'Speichern & Schließen',
+      soundEffects: 'Soundeffekte',
+      on: 'An',
+      off: 'Aus',
     },
     review: {
       meaning: 'Bedeutung',
@@ -239,6 +260,9 @@ const messages = {
       next: 'WEITER',
       sessionComplete: 'Sitzung beendet!',
       levelup: 'Du hast deine Kanji-Skills verbessert.',
+      levelsUp: '{n} aufgestiegen',
+      levelsDown: '{n} abgestiegen',
+      results: 'Ergebnisse',
       back: 'Zurück zur Sammlung',
       caughtUp: 'Alles erledigt!',
       noReviews: 'Gerade keine Reviews verfügbar.',
@@ -304,8 +328,13 @@ const messages = {
       learned: '{n}個の新しい漢字を覚えました。',
       components: '構成要素',
       observe: '書き順を見る',
+      replay: 'もう一度',
       trace: 'なぞる',
       drawStep: '書く ({n}/{total})',
+      sectionMeaning: '意味',
+      sectionMnemonic: '覚え方',
+      sectionReadings: '読み方',
+      learnedKanji: '学んだ漢字',
       backToDashboard: 'ダッシュボードに戻る',
     },
     hero: {
@@ -330,6 +359,7 @@ const messages = {
       next24: '今後24時間',
       availableNow: '今すぐ可能',
       inHours: '{n}時間後',
+      inDays: '{n}日後',
       noIncoming: '24時間以内のレビューはありません。',
       items: '個',
       reviewsCount: '{count} レビュー',
@@ -356,6 +386,9 @@ const messages = {
       strict: '厳しい',
       loose: '甘い',
       save: '保存して閉じる',
+      soundEffects: '効果音',
+      on: 'オン',
+      off: 'オフ',
     },
     review: {
       meaning: '意味',
@@ -369,6 +402,9 @@ const messages = {
       next: '次へ',
       sessionComplete: 'セッション完了！',
       levelup: '漢字力がアップしました。',
+      levelsUp: '{n}個昇格',
+      levelsDown: '{n}個降格',
+      results: '結果',
       back: 'コレクションに戻る',
       caughtUp: '完了しました！',
       noReviews: '現在レビューするものはありません。',