Add data models, randomization, and report factory setup

Introduced several new classes in the `EnvelopeGenerator.WebUI.Client` namespace:
- Added `Adjustment` class for financial adjustments with deterministic randomization.
- Added `Customer` class to load customer data from a SQL data source with fallback.
- Added `DataItem` class to represent detailed billing data, including adjustments.
- Added `DataItemList` class implementing `IList` for dynamic `DataItem` generation.
- Added `DeterministicRandom` class for reproducible random value generation.
- Added `Term` struct to define payment terms.
- Added `ReportsFactory` class to manage predefined reports.

Updated `MIGRATION_CONTEXT.md` to document the completion of Phase 5 (Data & PredefinedReports Migration) and outline next steps for resolving DevExpress-related errors in Phase 7.

EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI.Client/Data/Adjustment.cs

@@ -0,0 +1,44 @@
+namespace EnvelopeGenerator.WebUI.Client.Data {
+    public class Adjustment
+    {
+        public static Adjustment CreateBalanceForward(DateTime dt, int random)
+        {
+            var rnd = new DeterministicRandom(random);
+            Adjustment res = new Adjustment();
+            res.currentDateTime = dt;
+            res.currentDescription = "Balance Forward";
+            res.currentAmount = rnd.Random(10, 300) * 10;
+            return res;
+        }
+        public static Adjustment CreatePayment(DateTime dt, int random)
+        {
+            var rnd = new DeterministicRandom(random);
+            Adjustment res = new Adjustment();
+            res.currentDateTime = dt;
+            res.currentDescription = "Payment";
+            res.currentAmount = -rnd.Random(1, 40) * 10;
+            return res;
+        }
+        public static Adjustment CreateCharge(DateTime dt, int random)
+        {
+            var rnd = new DeterministicRandom(random);
+            Adjustment res = new Adjustment();
+            res.currentDateTime = dt;
+            res.currentDescription = rnd.GetRandomItem(bills);
+            res.currentAmount = rnd.Random(10, 50) * 10;
+            return res;
+        }
+
+        DateTime currentDateTime;
+        string currentDescription = "";
+        double currentAmount = 0;
+        static readonly string[] bills = new string[] { "Bill - Insurance", "Bill - Electricity", "Bill - Rent", "Bill - Phone", "Bill - Office Supplies" };
+        public DateTime Date { get { return currentDateTime; } }
+        public string Description { get { return currentDescription; } }
+        public double Amount { get { return currentAmount; } }
+
+        public Adjustment()
+        {
+        }
+    }
+}