Add tests, docs, and tools for TinyShop solution

Enhanced integration tests with in-memory database support and added code coverage tools (`coverlet.collector`).

- Introduced new test methods in `StoreUiTests.cs` to validate UI functionality, navigation, and responsive design.
- Added `CreateTestFactoriesWithProducts` helper for seeding test data.
- Created `TinyShopTest` MSTest project targeting .NET 10.0 with lifecycle methods and parallel test execution.
- Updated `IntegrationTests.csproj` with `Microsoft.EntityFrameworkCore.InMemory` and `coverlet.collector`.
- Added `dotnet-reportgenerator-globaltool` for HTML coverage reports.
- Documented the solution in `SOLUTION_GUIDE.md` with architecture, setup, and troubleshooting.
- Updated `VS2022-lab300.slnx` to include the new test project.

These changes improve test reliability, maintainability, and developer onboarding.

Author: ralphke

VS2022-lab300.slnx

@@ -0,0 +1,3 @@
+<Solution>
+  <Project Path="TinyShopTest/TinyShopTest.csproj" />
+</Solution>

src/.config/dotnet-tools.json

@@ -0,0 +1,13 @@
+{
+  "version": 1,
+  "isRoot": true,
+  "tools": {
+    "dotnet-reportgenerator-globaltool": {
+      "version": "5.4.4",
+      "commands": [
+        "reportgenerator"
+      ],
+      "rollForward": false
+    }
+  }
+}