Add E2E test for global.json paths-driven SDK install directory

[Copilot]

The existing InstallViaGlobalJson_SdkUsesGlobalJsonSource E2E test only covered version/rollForward in global.json — there was no test verifying that the paths field actually directs dotnetup to install the SDK into the specified local directory.

Changes

• New E2E test InstallViaGlobalJson_PathsDirectsSdkToLocalDirectory in LifecycleEndToEndTests:
  • Creates a global.json with "paths": [".dotnet"], "version": "9.0.103", and "rollForward": "disable"
  • Runs dotnetup sdk install without --install-path, exercising the InstallPathResolver path that falls through to GlobalJsonInfo.SdkPath
  • Asserts the SDK directory exists at <project-dir>/.dotnet/sdk/9.0.103/
  • Asserts the manifest records the root under the paths-resolved directory with InstallSource.GlobalJson and the correct GlobalJsonPath

{
  "sdk": {
    "version": "9.0.103",
    "rollForward": "disable",
    "paths": [".dotnet"]
  }
}

The implementation under test (GlobalJsonInfo.SdkPath, InstallPathResolver.Resolve) was already in place; this test closes the coverage gap.