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/FeatureMatcher.swift

@@ -0,0 +1,38 @@
+import Vision
+import CoreGraphics
+import ImageIO
+
+class FeatureMatcher {
+    static let revision = VNGenerateImageFeaturePrintRequest.Revision.revision1
+
+    static func generateFingerprint(from image: CGImage, orientation: CGImagePropertyOrientation = .up) async throws -> VNFeaturePrintObservation {
+        let req = VNGenerateImageFeaturePrintRequest()
+        req.revision = revision
+        req.imageCropAndScaleOption = .scaleFill
+        let handler = VNImageRequestHandler(cgImage: image, orientation: orientation, options: [:])
+        try handler.perform([req])
+
+        guard let result = req.results?.first as? VNFeaturePrintObservation else {
+            throw NSError(domain: "FeatureMatcher", code: -1, userInfo: [NSLocalizedDescriptionKey: "No features detected"])
+        }
+        return result
+    }
+
+    static func identify(scan: VNFeaturePrintObservation, database: [CardMetadata], cache: [UUID: VNFeaturePrintObservation]) -> MatchResult {
+        var candidates: [(CardMetadata, Float)] = []
+        for card in database {
+            guard let obs = cache[card.id] else { continue }
+            var dist: Float = 0
+            if (try? scan.computeDistance(&dist, to: obs)) != nil && dist < 18.0 {
+                candidates.append((card, dist))
+            }
+        }
+        let sorted = candidates.sorted { $0.1 < $1.1 }
+        guard let best = sorted.first else { return .unknown }
+
+        if best.1 < 6.0 { return .exact(best.0) }
+        let close = sorted.filter { $0.1 < (best.1 + 3.0) }
+        if close.count > 1 { return .ambiguous(name: best.0.name, candidates: close.map { $0.0 }) }
+        return .exact(best.0)
+    }
+}