fix: register DiagramOutputWriter in CLI integration test helper

[Copilot]

• Add DiagramOutputWriter singleton registration to CliTestHelpers.CreateApp()
• Remove UTF-8 BOM from DiagramOutputWriter.cs to fix dotnet format --verify-no-changes CHARSET error

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[Copilot]

Pull request overview

This PR fixes a dependency injection issue in the CLI integration test helper that was causing all CLI integration tests to fail. The DiagramOutputWriter service, which is injected into all three CLI commands (VisualizeCommand, ErdCommand, and ClassDiagramCommand), was registered in the production application but missing from the test setup.

Changes:

• Added DiagramOutputWriter singleton registration to the CLI test helper's CreateApp() method to match the production DI configuration in Program.cs

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[HandyS11]

@copilot the CI just failled with this error

Run dotnet format ProjGraph.slnx --no-restore --verify-no-changes
D:\a\ProjGraph\ProjGraph\src\ProjGraph.Cli\Infrastructure\DiagramOutputWriter.cs(1,1): error CHARSET: Fix file encoding. [D:\a\ProjGraph\ProjGraph\src\ProjGraph.Cli\ProjGraph.Cli.csproj]
Error: Process completed with exit code 1.

[Copilot]

@copilot the CI just failled with this error

Run dotnet format ProjGraph.slnx --no-restore --verify-no-changes
...

Fixed in commit e4b3f0a — DiagramOutputWriter.cs had a UTF-8 BOM which caused the CHARSET error. Stripped the BOM so the file is now plain UTF-8.