docs: 为 CLI、网页编排器和插件协议补充学习向注释

在核心类型、图执行器、stdio 插件和前端入口写清职责与对照路径，不改运行行为。

MAF1.Core/PluginContract/PluginManifest.cs

@@ -2,6 +2,10 @@ using System.Text.Json.Serialization;
 
 namespace MAF1.PluginContract;
 
+/// <summary>
+/// 每个插件目录里的 plugin.json。网页宿主扫描这个文件来画节点端口，不会加载插件 DLL。
+/// Id 会出现在画布节点的 Type 上。
+/// </summary>
 public sealed class PluginManifest
 {
     public string Id { get; set; } = "";
@@ -16,12 +20,14 @@ public sealed class PluginManifest
     public List<PluginPort> Outputs { get; set; } = [];
 }
 
+/// <summary>如何启动插件进程。Command 可以是相对插件目录的 exe，或 dotnet + dll。</summary>
 public sealed class PluginLaunch
 {
     public string Command { get; set; } = "";
     public List<string> Args { get; set; } = [];
 }
 
+/// <summary>画布上的一个输入或输出端口。Name 必须和代码里读写的字段一致。</summary>
 public sealed class PluginPort
 {
     public string Name { get; set; } = "";
@@ -30,6 +36,7 @@ public sealed class PluginPort
     public bool Required { get; set; }
 }
 
+/// <summary>插件声明「我需要哪种凭据」。宿主按 Type 注入，Key 不进流程图 JSON。</summary>
 public sealed class PluginCredentialNeed
 {
     public string Name { get; set; } = "";
@@ -38,6 +45,7 @@ public sealed class PluginCredentialNeed
     public string Description { get; set; } = "";
 }
 
+/// <summary>宿主写入插件 stdin 的整包请求：业务输入 + 凭据。</summary>
 public sealed class PluginRequest
 {
     public Dictionary<string, object?> Inputs { get; set; } = new(StringComparer.OrdinalIgnoreCase);
@@ -46,6 +54,7 @@ public sealed class PluginRequest
     public Dictionary<string, PluginCredentialPayload> Credentials { get; set; } = new(StringComparer.OrdinalIgnoreCase);
 }
 
+/// <summary>实际的 endpoint / apiKey / model。只在宿主→插件进程之间传递。</summary>
 public sealed class PluginCredentialPayload
 {
     public string Id { get; set; } = "";
@@ -56,6 +65,7 @@ public sealed class PluginCredentialPayload
     public Dictionary<string, string> Extra { get; set; } = new(StringComparer.OrdinalIgnoreCase);
 }
 
+/// <summary>插件 JSON 统一 camelCase，和网页前端字段名对齐。</summary>
 public static class PluginJson
 {
     public static readonly System.Text.Json.JsonSerializerOptions Options = new()