feat: AI 模型支持 On-Demand Resources 按需下载

- 新增 ODRManager 管理模型资源下载
- EditorView 添加下载进度 UI
- Package.swift 移除内嵌模型资源
- 减小应用包体积约 64MB

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

to-live-photo/to-live-photo/Views/EditorView.swift

@@ -37,6 +37,9 @@ struct EditorView: View {
 
     // AI 超分辨率
     @State private var aiEnhanceEnabled: Bool = false
+    @State private var aiModelNeedsDownload: Bool = false
+    @State private var aiModelDownloading: Bool = false
+    @State private var aiModelDownloadProgress: Double = 0
 
     // 视频诊断
     @State private var videoDiagnosis: VideoDiagnosis?
@@ -370,10 +373,45 @@ struct EditorView: View {
                 }
             }
             .tint(.purple)
-            .disabled(!AIEnhancer.isAvailable())
+            .disabled(!AIEnhancer.isAvailable() || aiModelDownloading)
+            .onChange(of: aiEnhanceEnabled) { _, newValue in
+                if newValue {
+                    checkAndDownloadModel()
+                }
+            }
 
-            if aiEnhanceEnabled {
+            // 模型下载进度
+            if aiModelDownloading {
+                VStack(alignment: .leading, spacing: 8) {
+                    HStack(spacing: 8) {
+                        ProgressView()
+                            .scaleEffect(0.8)
+                        Text("正在下载 AI 模型...")
+                            .font(.caption)
+                            .foregroundStyle(.secondary)
+                    }
+                    
+                    ProgressView(value: aiModelDownloadProgress)
+                        .tint(.purple)
+                    
+                    Text(String(format: "%.0f%%", aiModelDownloadProgress * 100))
+                        .font(.caption2)
+                        .foregroundStyle(.secondary)
+                }
+                .padding(.leading, 4)
+            }
+
+            if aiEnhanceEnabled && !aiModelDownloading {
                 VStack(alignment: .leading, spacing: 6) {
+                    if aiModelNeedsDownload {
+                        HStack(spacing: 4) {
+                            Image(systemName: "arrow.down.circle")
+                                .foregroundStyle(.orange)
+                                .font(.caption)
+                            Text("首次使用需下载 AI 模型（约 64MB）")
+                                .font(.caption)
+                        }
+                    }
                     HStack(spacing: 4) {
                         Image(systemName: "sparkles")
                             .foregroundStyle(.purple)
@@ -415,6 +453,10 @@ struct EditorView: View {
         .padding(16)
         .background(Color.purple.opacity(0.1))
         .clipShape(RoundedRectangle(cornerRadius: 12))
+        .task {
+            // 检查模型是否需要下载
+            aiModelNeedsDownload = await AIEnhancer.needsDownload()
+        }
     }
 
     // MARK: - 兼容模式开关
@@ -681,6 +723,46 @@ struct EditorView: View {
         return CropRect(x: cropX, y: cropY, width: cropWidth, height: cropHeight)
     }
 
+    private func checkAndDownloadModel() {
+        guard aiEnhanceEnabled else { return }
+        
+        Task {
+            // 检查是否需要下载
+            let needsDownload = await AIEnhancer.needsDownload()
+            
+            await MainActor.run {
+                aiModelNeedsDownload = needsDownload
+            }
+            
+            if needsDownload {
+                await MainActor.run {
+                    aiModelDownloading = true
+                    aiModelDownloadProgress = 0
+                }
+                
+                do {
+                    try await AIEnhancer.downloadModel { progress in
+                        Task { @MainActor in
+                            aiModelDownloadProgress = progress
+                        }
+                    }
+                    
+                    await MainActor.run {
+                        aiModelDownloading = false
+                        aiModelNeedsDownload = false
+                    }
+                } catch {
+                    await MainActor.run {
+                        aiModelDownloading = false
+                        // 下载失败时禁用 AI 增强
+                        aiEnhanceEnabled = false
+                    }
+                    print("Failed to download AI model: \(error)")
+                }
+            }
+        }
+    }
+
     private func startProcessing() {
         Analytics.shared.log(.editorGenerateClick, parameters: [
             "trimStart": trimStart,