Implement storage architecture from ai_blueprint.md

Primary sync: replace PersistenceActor JSON file with SwiftData + CloudKit
- Add SavedCardModel (@Model class) and PersistenceController (ModelContainer
  with .automatic CloudKit, fallback to local). BackgroundPersistenceActor
  (@ModelActor) handles all DB I/O off the main thread.
- One-time migration imports user_collection.json into SwiftData and renames
  the original file to prevent re-import.
- Inject modelContainer into SwiftUI environment in IYmtgApp.

Image storage: Documents/UserContent/ subfolder (blueprint requirement)
- ImageManager.dir now targets iCloud Documents/UserContent/ (or local equiv).
- migrateImagesToUserContent() moves existing JPGs to the new subfolder on
  first launch; called during the SwiftData migration.

Firebase: demoted to optional manual backup (metadata only, no images)
- Remove all automatic CloudEngine.save/delete/batchUpdatePrices calls from
  CollectionViewModel mutations.
- Add backupAllToFirebase() for user-triggered metadata sync.
- Add isFirebaseBackupEnabled to AppConfig (default false).
- Add Cloud Backup section in Library settings with iCloud vs Firebase
  explanation and "Backup Metadata to Firebase Now" button.

Also: full modular refactor (Data/, Features/, Services/ directories) and
README updated with CloudKit setup steps and revised release checklist.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

IYmtg_App_iOS/Services/Vision/Heuristics/SaturationDetector.swift

@@ -0,0 +1,30 @@
+import CoreImage
+import CoreGraphics
+
+// MARK: - SATURATION DETECTOR (Unlimited vs Revised)
+class SaturationDetector {
+    static func analyze(image: CGImage, orientation: CGImagePropertyOrientation = .up) -> Double {
+        // Crop to center 50% to analyze artwork saturation, ignoring borders
+        let ciImage = CIImage(cgImage: image).oriented(orientation)
+        let width = ciImage.extent.width
+        let height = ciImage.extent.height
+        let cropRect = CGRect(x: width * 0.25, y: height * 0.25, width: width * 0.5, height: height * 0.5)
+
+        let vector = CIVector(cgRect: cropRect)
+        guard let filter = CIFilter(name: "CIAreaAverage", parameters: [kCIInputImageKey: ciImage, kCIInputExtentKey: vector]),
+              let output = filter.outputImage else { return 0 }
+
+        var bitmap = [UInt8](repeating: 0, count: 4)
+        let context = SharedEngineResources.context
+        context.render(output, toBitmap: &bitmap, rowBytes: 4, bounds: CGRect(x: 0, y: 0, width: 1, height: 1), format: .RGBA8, colorSpace: nil)
+
+        // Simple Saturation approximation: (Max - Min) / Max
+        let r = Double(bitmap[0]) / 255.0
+        let g = Double(bitmap[1]) / 255.0
+        let b = Double(bitmap[2]) / 255.0
+        let maxC = max(r, max(g, b))
+        let minC = min(r, min(g, b))
+
+        return maxC == 0 ? 0 : (maxC - minC) / maxC
+    }
+}