Add full app source

Adds the Flutter inventory app source, cleaned up for a shared repo:
generic package name, no hardcoded ERP endpoints (moved to gitignored
local config), no dead auth code, no debug logging of session data.

lib/models/tracking_number.dart

@@ -0,0 +1,35 @@
+import 'package:inventory_app/models/product.dart';
+
+class TrackingNumber {
+  int? id;
+  int? version;
+  String? trackingNumberSeq;
+  String? perishableExpirationDate;
+  Product? product;
+
+  TrackingNumber({
+    this.id,
+    this.version,
+    this.trackingNumberSeq,
+    this.perishableExpirationDate,
+    this.product,
+  });
+
+  TrackingNumber.fromJson(Map<String, dynamic> json) {
+    id = json['id'];
+    version = json['version'];
+    trackingNumberSeq = json['trackingNumberSeq'];
+    perishableExpirationDate = json['perishableExpirationDate'];
+    product = json['product'];
+  }
+
+  Map<String, dynamic> toJson() {
+    final Map<String, dynamic> data = new Map<String, dynamic>();
+    data['id'] = this.id;
+    data['version'] = this.version;
+    data['trackingNumberSeq'] = this.trackingNumberSeq;
+    data['perishableExpirationDate'] = this.perishableExpirationDate;
+    data['product'] = this.product;
+    return data;
+  }
+}