Add .NET/C# instructions to multi-language workflows

[ViktorHofer]

Fixes #16152

[Copilot]

Pull request overview

Updates several agent workflow prompts/pattern docs to better support .NET/C# repositories, so multi-language workflows behave more correctly out of the box (per issue #16152).

Changes:

• Expanded “test file” pattern matching to include common C# test filenames in metrics/counting instructions.
• Included .csproj as a recognized build/dependency manifest in workflow heuristics.
• Added .NET/C# development and validation commands (e.g., dotnet test, dotnet build) to the Code Simplifier workflow guidance.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
.github/workflows/shared/metrics-patterns.md	Extends test-file patterns used for LOC/test metrics to include C# tests.
.github/workflows/repository-quality-improver.md	Updates test counting and security grep includes to account for C# files.
.github/workflows/repo-audit-analyzer.md	Treats *.csproj as a build/test indicator alongside other ecosystem manifests.
.github/workflows/pr-triage-agent.md	Updates PR categorization heuristics to recognize C# tests and project files.
.github/workflows/copilot-pr-merged-report.md	Adds C# test file patterns to reporting instructions/templates.
.github/workflows/code-simplifier.md	Adds .NET/C# coding standards guidance and dotnet CLI validation steps.
.github/workflows/bot-detection.md	Extends “dependency manifests” risk scoring to include .NET manifest files.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[ViktorHofer]

Thanks for approving @pelikhan. Feel free to merge. I won't push any further commits.