Add dotnet format check to CI pipeline

[LeeCampbell]

Summary

Add a dotnet format --verify-no-changes step to the GitHub Actions CI workflow so that code style is enforced on every PR.

Details

Add a step to .github/workflows/ci.yml that runs:

- name: Check code formatting
  run: dotnet format --verify-no-changes --verbosity diagnostic

This should run after dotnet restore but before dotnet build, so contributors get fast feedback on formatting issues without waiting for a full build.

The step will fail the CI check if any code doesn't match the .editorconfig rules, giving contributors a clear signal of what to fix.

Acceptance Criteria

• dotnet format --verify-no-changes step added to CI workflow
• Step runs on all PR builds
• CI passes on the current codebase (requires the format fix issue to be completed first)
• Failure output clearly indicates which files need formatting

Dependencies

• Depends on Add .editorconfig with project coding conventions #114 (.editorconfig) being in place
• Depends on Run dotnet format to fix existing code to match .editorconfig #115 (bulk dotnet format pass) being completed

[leecampbell-codeagent]

PR created: #152