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/Features/Study/CardRenderer.swift

@@ -0,0 +1,88 @@
+import SwiftUI
+
+/// Rendert die Karten-Inhalte je nach `CardType`. Front-/Back-Seite
+/// werden über `isFlipped` gesteuert.
+///
+/// β-2 deckt `basic`, `basic-reverse`, `cloze` ab. Restliche Typen
+/// zeigen einen Placeholder mit Hinweis auf die kommende Phase.
+struct CardRenderer: View {
+    let card: ReviewCard
+    let subIndex: Int
+    let isFlipped: Bool
+
+    var body: some View {
+        Group {
+            switch card.type {
+            case .basic:
+                basicView(front: "front", back: "back")
+            case .basicReverse:
+                // sub_index 0 = front→back, sub_index 1 = back→front
+                if subIndex == 0 {
+                    basicView(front: "front", back: "back")
+                } else {
+                    basicView(front: "back", back: "front")
+                }
+            case .cloze:
+                clozeView
+            case .imageOcclusion, .audioFront, .typing, .multipleChoice:
+                placeholderView
+            }
+        }
+        .padding(24)
+        .frame(maxWidth: .infinity, maxHeight: .infinity)
+    }
+
+    @ViewBuilder
+    private func basicView(front frontKey: String, back backKey: String) -> some View {
+        VStack(spacing: 16) {
+            text(card.fields[frontKey] ?? "")
+                .font(.title2)
+                .foregroundStyle(CardsTheme.foreground)
+            if isFlipped {
+                Divider().background(CardsTheme.border)
+                text(card.fields[backKey] ?? "")
+                    .font(.title3)
+                    .foregroundStyle(CardsTheme.mutedForeground)
+            }
+        }
+    }
+
+    @ViewBuilder
+    private var clozeView: some View {
+        let raw = card.fields["text"] ?? ""
+        let clusterId = Cloze.clusterId(for: raw, subIndex: subIndex) ?? 1
+        let rendered = isFlipped
+            ? Cloze.renderAnswer(raw, activeClusterId: clusterId)
+            : Cloze.renderPrompt(raw, activeClusterId: clusterId)
+        VStack(spacing: 12) {
+            text(rendered)
+                .font(.title3)
+                .foregroundStyle(CardsTheme.foreground)
+        }
+    }
+
+    @ViewBuilder
+    private var placeholderView: some View {
+        VStack(spacing: 8) {
+            Image(systemName: "questionmark.square.dashed")
+                .font(.largeTitle)
+                .foregroundStyle(CardsTheme.mutedForeground)
+            Text("Card-Type »\(card.type.rawValue)« kommt in einer späteren Phase")
+                .font(.caption)
+                .multilineTextAlignment(.center)
+                .foregroundStyle(CardsTheme.mutedForeground)
+        }
+    }
+
+    /// Markdown-Bold (`**...**`) wird auf SwiftUI's AttributedString gemappt.
+    private func text(_ markdown: String) -> some View {
+        let attributed = (try? AttributedString(
+            markdown: markdown,
+            options: AttributedString.MarkdownParsingOptions(
+                interpretedSyntax: .inlineOnlyPreservingWhitespace
+            )
+        )) ?? AttributedString(markdown)
+        return Text(attributed)
+            .multilineTextAlignment(.center)
+    }
+}