.NET: Inline const values in samples where used only once

[westey-m]

Motivation and Context

#1163

Description

• Inline const literals in samples where they are only used once, to simplify the samples.

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.

[Copilot]

Pull Request Overview

This PR inlines constant string literals in sample code where they are only used once, improving code simplicity and readability by removing unnecessary constant declarations.

• Removes const string declarations for agent names and instructions
• Inlines these values directly at their single usage points
• Uses named parameters to improve clarity when passing inline values

Reviewed Changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
FoundryAgent_Hosted_MCP/Program.cs	Inlined AgentName and AgentInstructions constants in agent creation
Agent_Step16_ChatReduction/Program.cs	Inlined JokerName and JokerInstructions constants in agent options
Agent_Step15_Plugins/Program.cs	Inlined AgentName and AgentInstructions constants in agent creation
Agent_Step10_AsMcpTool/Program.cs	Inlined JokerName, JokerDescription, and JokerInstructions constants
Agent_Step09_DependencyInjection/Program.cs	Inlined constants and added named parameters for clarity
Agent_Step08_Observability/Program.cs	Inlined constants and added named parameters in agent creation
Agent_Step07_3rdPartyThreadStorage/Program.cs	Inlined constants in agent options configuration
Agent_Step06_PersistedConversations/Program.cs	Inlined constants and added named parameters in agent creation
Agent_Step02_MultiturnConversation/Program.cs	Inlined constants and added named parameters in agent creation
Agent_Step01_Running/Program.cs	Inlined constants and added named parameters in agent creation
Agent_OpenAI_Step01_Running/Program.cs	Inlined constants and added named parameters in agent creation
Agent_With_OpenAIResponses/Program.cs	Inlined constants and added named parameters in agent creation
Agent_With_OpenAIChatCompletion/Program.cs	Inlined constants and added named parameters in agent creation
Agent_With_Ollama/Program.cs	Inlined constants and added named parameters in agent creation
Agent_With_ONNX/Program.cs	Inlined constants and added named parameters in agent creation
Agent_With_AzureOpenAIResponses/Program.cs	Inlined constants and added named parameters in agent creation
Agent_With_AzureOpenAIChatCompletion/Program.cs	Inlined constants and added named parameters in agent creation
Agent_With_AzureFoundryModel/Program.cs	Inlined constants and added named parameters in agent creation

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