Clean up namespaces (#410)

No meaningful code changes, just lots of namespace shuffling to have fewer namespaces and to put things in better namespaces.

src/ModelContextProtocol/Protocol/Prompt.cs

@@ -0,0 +1,50 @@
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Represents a prompt that the server offers.
+/// </summary>
+/// <remarks>
+/// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for details.
+/// </remarks>
+public class Prompt
+{
+    /// <summary>
+    /// Gets or sets a list of arguments that this prompt accepts for templating and customization.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This list defines the arguments that can be provided when requesting the prompt.
+    /// Each argument specifies metadata like name, description, and whether it's required.
+    /// </para>
+    /// <para>
+    /// When a client makes a <see cref="RequestMethods.PromptsGet"/> request, it can provide values for these arguments
+    /// which will be substituted into the prompt template or otherwise used to render the prompt.
+    /// </para>
+    /// </remarks>
+    [JsonPropertyName("arguments")]
+    public List<PromptArgument>? Arguments { get; set; }
+
+    /// <summary>
+    /// Gets or sets an optional description of what this prompt provides.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This description helps developers understand the purpose and use cases for the prompt.
+    /// It should explain what the prompt is designed to accomplish and any important context.
+    /// </para>
+    /// <para>
+    /// The description is typically used in documentation, UI displays, and for providing context
+    /// to client applications that may need to choose between multiple available prompts.
+    /// </para>
+    /// </remarks>
+    [JsonPropertyName("description")]
+    public string? Description { get; set; }
+
+    /// <summary>
+    /// Gets or sets the name of the prompt.
+    /// </summary>
+    [JsonPropertyName("name")]
+    public string Name { get; set; } = string.Empty;
+}