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/RemoteImage.swift

@@ -0,0 +1,70 @@
+import SwiftUI
+
+#if canImport(UIKit)
+import UIKit
+#elseif canImport(AppKit)
+import AppKit
+#endif
+
+/// Lädt ein authentifiziertes Image vom Cardecky-Media-Endpoint und
+/// rendert es. Streamt erst beim ersten Mal, danach aus dem
+/// MediaCache (LRU 200 MB).
+struct RemoteImage: View {
+    let mediaId: String
+    let contentMode: ContentMode
+
+    @Environment(\.mediaCache) private var mediaCache
+    @State private var image: PlatformImage?
+    @State private var failed = false
+
+    init(mediaId: String, contentMode: ContentMode = .fit) {
+        self.mediaId = mediaId
+        self.contentMode = contentMode
+    }
+
+    var body: some View {
+        Group {
+            if let image {
+                imageView(image)
+            } else if failed {
+                ContentUnavailableView("Bild konnte nicht geladen werden", systemImage: "photo.badge.exclamationmark")
+                    .foregroundStyle(CardsTheme.mutedForeground)
+            } else {
+                ProgressView()
+                    .tint(CardsTheme.primary)
+            }
+        }
+        .task(id: mediaId) {
+            await load()
+        }
+    }
+
+    @ViewBuilder
+    private func imageView(_ image: PlatformImage) -> some View {
+        #if canImport(UIKit)
+        Image(uiImage: image).resizable().aspectRatio(contentMode: contentMode)
+        #elseif canImport(AppKit)
+        Image(nsImage: image).resizable().aspectRatio(contentMode: contentMode)
+        #endif
+    }
+
+    private func load() async {
+        guard let cache = mediaCache else { failed = true; return }
+        do {
+            let data = try await cache.data(for: mediaId)
+            if let img = PlatformImage(data: data) {
+                image = img
+            } else {
+                failed = true
+            }
+        } catch {
+            failed = true
+        }
+    }
+}
+
+#if canImport(UIKit)
+typealias PlatformImage = UIImage
+#elseif canImport(AppKit)
+typealias PlatformImage = NSImage
+#endif