Clarify dotnet run behavior with project files

[jjonescz]

See dotnet/sdk#52494 (comment).

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[Copilot]

Pull request overview

This pull request clarifies the behavior of dotnet run when used with file-based apps in the presence of project files. The change addresses potential confusion users might experience when a project file exists in the same directory as their file-based app.

Changes:

• Added a NOTE callout explaining that dotnet run file.cs (without the --file option) will prioritize project files over file-based apps when both exist in the current directory