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/DeterministicRandom.cs

@@ -0,0 +1,60 @@
+namespace EnvelopeGenerator.WebUI.Client.Data {
+    class DeterministicRandom {
+        const int randomCount = 10000;
+        static readonly int[] deterministicRandomNumbers;
+        static readonly DateTime time;
+        int rnd;
+        int Next {
+            get {
+                rnd = deterministicRandomNumbers[rnd % randomCount];
+                return rnd;
+            }
+        }
+        public char RandomChar {
+            get {
+                return (char)((int)'A' + Random(0, 26));
+            }
+        }
+        public int[] RandomList(int count, int to) {
+            int[] res = new int[count];
+            for(int i = 0; i < Math.Min(count, to); i++)
+                res[i] = i;
+            for(int i = to; i < count; i++)
+                res[i] = Random(to);
+
+            for(int i = 0; i < count; i++) {
+                int ind = Random(count);
+                int temp = res[ind];
+                res[ind] = res[i];
+                res[i] = temp;
+            }
+            return res;
+        }
+        public int Random(int to) {
+            return Random(0, to);
+        }
+        public int Random(int from, int to) {
+            return Next % Math.Max(1, to - from) + from;
+        }
+        public T GetRandomItem<T>(IList<T> list) {
+            return list[Next % list.Count];
+        }
+        public DateTime RandomTime() {
+            return RandomTime(time, 0, 30 * 24);
+        }
+        public DateTime RandomTime(DateTime from, int fromHours, int toHours) {
+            return from.AddHours(Next % (toHours - fromHours) + fromHours);
+        }
+
+        static DeterministicRandom() {
+            time = DateTime.Now.AddDays(-62);
+            Random currentRandom = new Random(randomCount);
+            deterministicRandomNumbers = new int[randomCount];
+            for(int i = 0; i < randomCount; i++)
+                deterministicRandomNumbers[i] = currentRandom.Next(randomCount);
+        }
+        public DeterministicRandom(int i) {
+            this.rnd = i + (i >> 10) + (i >> 20);
+        }
+    }
+}