refactor: GitHub application integration - #19

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v2, actions/setup-dotnet@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Non-nullable property 'TopicsRepository' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'DiscourseClient' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'GitHubApiClient' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

'MockInnerHandler.Send(HttpRequestMessage, CancellationToken)' hides inherited member 'HttpMessageHandler.Send(HttpRequestMessage, CancellationToken)'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.

Non-nullable property 'TopicsRepository' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'DiscourseClient' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'GitHubApiClient' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.