Add 6 Anton-inspired features for vocabulary learning

Feature 1 — StarRating: 1-3 stars per exercise (100%=3, 70%=2, <70%=1)
Feature 2 — Progress bar in UnitCard with Leitner box distribution
Feature 3 — Listening exercise: hear word via TTS, choose correct translation
Feature 4 — Matching game: tap-to-match EN↔DE pairs (6 per round)
Feature 5 — Pronunciation: word with syllable bows + mic → STT comparison
Feature 6 — Syllable bows in FlashCards (SyllableBow under word + IPA)

UnitCard now shows 6 exercise types: Karten, Quiz, Tippen, Hoeren,
Zuordnen, Sprechen. Progress bar and star count displayed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

studio-v2/components/learn/FlashCard.tsx

@@ -103,9 +103,14 @@ export function FlashCard({
             <span className={`text-xs font-medium mb-4 ${isDark ? 'text-blue-300/60' : 'text-blue-500'}`}>
               DEUTSCH
             </span>
+            {syllablesBack && syllablesBack.length > 0 ? (
+              <SyllableBow word={back} syllables={syllablesBack} isDark={isDark} size="md" />
+            ) : (
               <span className={`text-3xl font-bold text-center ${isDark ? 'text-white' : 'text-slate-900'}`}>
                 {back}
               </span>
+            )}
+            {ipaBack && <span className={`text-sm mt-2 ${isDark ? 'text-blue-300/40' : 'text-blue-400'}`}>{ipaBack}</span>}
           </div>
         </div>
       </div>