.NET: fix: Add missing Workflows "Shared" sources to solution

[Jacob Alber (lokitoth)]

Some of the "Shared" sources were missing from the solution. Add them.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

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Pull request overview

This PR updates the .NET solution file to include the previously omitted src/Shared/Workflows sources under Solution Items, so those shared workflow helper files are visible in the solution alongside the rest of the shared source tree.

Changes:

• Adds the src/Shared/Workflows solution folder entry.
• Includes the Execution shared workflow files in Solution Items.
• Includes the Settings shared workflow files in Solution Items.