v0.3.0 — Phase β-2 Study-Loop

Voller Lern-Flow mit Web-Parität: fällige Karten via /reviews/due
laden, flip + rate (4 Buttons + Haptic), Grades via Offline-Queue
ans Server-FSRS schicken.

- Card/Review/DueReview DTOs mit snake_case + camelCase-deckId-
  Sonderfall im embedded card-Subobjekt
- CardType-Enum (alle 7 Typen), Rating-Enum mit deutschen Labels
- Cloze-Helper 1:1-Port aus cards-domain (extractClusterIds,
  subIndexCount, clusterId, renderPrompt/Answer, hint)
- CardsAPI.dueReviews(deckId:) + gradeReview(cardId,subIndex,rating,reviewedAt)
- PendingGrade SwiftData-Model + GradeQueue (FIFO-Drain, originaler
  Timestamp bleibt, bei Netzfehler in Queue, Retry beim nächsten Drain)
- StudySession @Observable State-Machine
- CardRenderer für basic, basic-reverse, cloze; Placeholder für
  image-occlusion/audio-front/typing/multiple-choice (β-3/β-4)
- RatingBar mit UIImpactFeedbackGenerator (medium/heavy)
- StudySessionView per NavigationLink aus DeckListView
- 9 neue Tests (Cloze: 8, Review-Decoding: 3), insgesamt 17 grün

Server-authoritative FSRS bleibt — kein ts-fsrs-Port.
Endurance-Test auf realem Gerät steht aus (siehe PLAN.md).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Sources/Core/API/CardsAPI.swift

@@ -54,6 +54,46 @@ actor CardsAPI {
         return try decoder.decode(DueReviewsResponse.self, from: data).total
     }
 
+    // MARK: - Study
+
+    /// `GET /api/v1/reviews/due?deck_id=...&limit=500` — fällige Reviews
+    /// inklusive zugehöriger Card-Daten. Hot-Path für die Study-View.
+    func dueReviews(deckId: String, limit: Int = 500) async throws -> [DueReview] {
+        let (data, http) = try await transport.request(
+            path: "/api/v1/reviews/due?deck_id=\(deckId)&limit=\(limit)"
+        )
+        try ensureOK(http, data: data)
+        return try decoder.decode(DueReviewsListResponse.self, from: data).reviews
+    }
+
+    /// `POST /api/v1/reviews/:cardId/:subIndex/grade` — gibt eine
+    /// Bewertung ab. Server rechnet FSRS, antwortet mit aktualisiertem
+    /// Review.
+    @discardableResult
+    func gradeReview(
+        cardId: String,
+        subIndex: Int,
+        rating: Rating,
+        reviewedAt: Date = .now
+    ) async throws -> Review {
+        let body = try makeJSON(GradeReviewBody(rating: rating, reviewedAt: reviewedAt))
+        let (data, http) = try await transport.request(
+            path: "/api/v1/reviews/\(cardId)/\(subIndex)/grade",
+            method: "POST",
+            body: body
+        )
+        try ensureOK(http, data: data)
+        return try decoder.decode(Review.self, from: data)
+    }
+
+    // MARK: - JSON-Encoding
+
+    private func makeJSON<T: Encodable>(_ value: T) throws -> Data {
+        let encoder = JSONEncoder()
+        encoder.dateEncodingStrategy = .iso8601
+        return try encoder.encode(value)
+    }
+
     // MARK: - Helpers
 
     private func ensureOK(_ http: HTTPURLResponse, data: Data) throws {