v0.5.0 — Phase β-4 Media + Advanced Card-Types

Alle 7 Card-Types werden gerendert und können erstellt werden.
image-occlusion mit Touch-Drag-Mask-Editor (kein PencilKit — Server-
Schema erlaubt nur Rechtecke), audio-front mit AVAudioPlayer und
File-Picker.

- MediaUploadResponse-DTO, MaskRegion-Codable mit 0..1-Coordinates
- MaskRegions.parse/encode (1:1-Port aus cards-domain, Sortierung
  nach ID lexikographisch)
- CardFieldsBuilder.imageOcclusion mit stringified-JSON-mask_regions
  + audioFront
- CardsAPI.uploadMedia (Multipart, 25 MiB) + fetchMedia (streamed)
- MediaCache actor mit LRU 200 MB (contentModificationDate-Eviction)
- mediaCache Environment-Key
- RemoteImage + AudioPlayerButton SwiftUI-Views
- CardRenderer: imageOcclusion (Mask-Overlay über RemoteImage) +
  audioFront (AudioPlayerButton + back-Text auf Flip)
- MaskEditorView: Touch-Drag-Rechteck, Label-Edit, Delete
- CardEditorView erweitert: PhotosPicker für Image, fileImporter
  für Audio, Magic-Byte-MIME-Detection
- 6 neue Tests für MaskRegions (30 Total grün)

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

Sources/Features/Media/AudioPlayerButton.swift

@@ -0,0 +1,73 @@
+import AVFoundation
+import SwiftUI
+
+/// Audio-Wiedergabe-Button für `audio-front`-Karten. Lädt das File einmal
+/// per MediaCache, spielt mit AVAudioPlayer ab.
+struct AudioPlayerButton: View {
+    let mediaId: String
+
+    @Environment(\.mediaCache) private var mediaCache
+    @State private var player: AVAudioPlayer?
+    @State private var isPlaying = false
+    @State private var failed = false
+
+    var body: some View {
+        Button {
+            togglePlayback()
+        } label: {
+            HStack(spacing: 12) {
+                Image(systemName: failed
+                    ? "speaker.slash.fill"
+                    : (isPlaying ? "pause.circle.fill" : "play.circle.fill"))
+                    .font(.system(size: 48))
+                    .foregroundStyle(failed ? CardsTheme.error : CardsTheme.primary)
+                Text(failed ? "Audio nicht verfügbar" : (isPlaying ? "Wiedergabe läuft" : "Anhören"))
+                    .font(.headline)
+                    .foregroundStyle(CardsTheme.foreground)
+            }
+            .frame(maxWidth: .infinity)
+            .padding(20)
+            .background(CardsTheme.surface, in: RoundedRectangle(cornerRadius: 12))
+            .overlay(
+                RoundedRectangle(cornerRadius: 12)
+                    .stroke(CardsTheme.border, lineWidth: 1)
+            )
+        }
+        .buttonStyle(.plain)
+        .disabled(failed)
+        .task(id: mediaId) {
+            await load()
+        }
+        .onDisappear {
+            player?.stop()
+            isPlaying = false
+        }
+    }
+
+    private func load() async {
+        guard let cache = mediaCache else { failed = true; return }
+        do {
+            let data = try await cache.data(for: mediaId)
+            #if canImport(UIKit)
+            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default)
+            try AVAudioSession.sharedInstance().setActive(true)
+            #endif
+            player = try AVAudioPlayer(data: data)
+            player?.prepareToPlay()
+        } catch {
+            failed = true
+        }
+    }
+
+    private func togglePlayback() {
+        guard let player else { return }
+        if player.isPlaying {
+            player.pause()
+            isPlaying = false
+        } else {
+            player.currentTime = 0
+            player.play()
+            isPlaying = true
+        }
+    }
+}