fix: Study Session card-flip UX, animations & deck title

[jvsena42]

Summary

Polishes the Study Session screen (StudySessionScreen) to better match the Pencil design (03 Study Session — front w1CAm / back aLoMj) and improves its motion and robustness.

Changes

• Design fidelity: removed the in-card TAP TO REVEAL label on the front; added a muted flip-hint row (↻ Tap card to reveal answer) below the card, shown on the front only. Tuned type sizes to the design (front prompt 48sp, back answer 42sp, card label 14sp / 1.5 letter-spacing).
• Card flip: slowed the flip from 450ms → 700ms with FastOutSlowInEasing; still snaps instantly when the OS has animations disabled.
• Difficulty buttons: added a staggered fade + rise + scale entrance on reveal and a press-scale feedback; both respect reduce-motion. Labels now auto-size (TextAutoSize) to stay on one line in the narrow buttons.
• Deck title in the header: the title now renders on a single, centered, ellipsized line taking the available width. Fixed it being blank on a cold cache — StudySessionViewModel now resolves the title via getLocal and falls back to listOwned() (per-card for multi-deck sessions).

Testing

• ./gradlew :composeApp:assembleDebug ✅
• ./gradlew :shared:compileKotlinMetadata ✅
• ./gradlew :shared:allTests ✅
• ./gradlew detektAll ✅

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