feat: add iOS support and harden receipt scanning

app/ios/ScanReceipts/Networking/APIEnvironment.swift

@@ -0,0 +1,30 @@
+import Foundation
+
+/// Which backend the app talks to. All three point at the *same* Next.js API
+/// described in `app/ios/README.md` — there is no separate mobile backend.
+enum APIEnvironment {
+    case production
+    case local
+
+    var baseURL: URL {
+        switch self {
+        case .production:
+            // TODO: swap for the real production domain before release.
+            return URL(string: "https://scan-receipts.app")!
+        case .local:
+            // Matches `dev-verify` in the web repo's .claude/launch.json (port
+            // 3901) so the app can be pointed at a live local backend without
+            // colliding with the docker-compose stack on 3000. Only reachable
+            // from an iOS Simulator on the same machine, not a physical device.
+            return URL(string: "http://localhost:3901")!
+        }
+    }
+
+    static var current: APIEnvironment {
+        #if DEBUG
+        return .local
+        #else
+        return .production
+        #endif
+    }
+}