refactor(rag): 更新AI模型和RAG端点的权限控制

- 移除FastEndpoints命名空间引用
- 移除Microsoft.Extensions.AI命名空间引用
- 将AI模型端点的AllowAnonymous替换为ai-model:read权限
- 将AI模型创建、更新、删除端点的AllowAnonymous替换为ai-model:write权限
- 将RAG流查询端点的AllowAnonymous替换为rag:query权限
- 统一端点安全性配置以符合权限管理要求

src/BuildFlow.Host/Endpoints/rag/AiModel/AiModelEndpoints.cs

@@ -1,4 +1,3 @@
-using FastEndpoints;
 using MediatR;
 using BuildFlow.Application.AiModel.Commands;
 using BuildFlow.Application.AiModel.DTOs;
@@ -12,7 +11,7 @@ public class GetAiModelsEndpoint(IMediator mediator) : EndpointWithoutRequest<Li
     public override void Configure()
     {
         Get("/ai/models");
-        AllowAnonymous();
+        Permissions("ai-model:read");
     }
 
     public override async Task HandleAsync(CancellationToken ct)
@@ -30,7 +29,7 @@ public class CreateAiModelEndpoint(IMediator mediator) : Endpoint<CreateAiModelR
     public override void Configure()
     {
         Post("/ai/models");
-        AllowAnonymous();
+        Permissions("ai-model:write");
     }
 
     public override async Task HandleAsync(CreateAiModelRequest req, CancellationToken ct)
@@ -48,7 +47,7 @@ public class UpdateAiModelEndpoint(IMediator mediator) : Endpoint<UpdateAiModelR
     public override void Configure()
     {
         Put("/ai/models/{Id}");
-        AllowAnonymous();
+        Permissions("ai-model:write");
     }
 
     public override async Task HandleAsync(UpdateAiModelRequest req, CancellationToken ct)
@@ -67,7 +66,7 @@ public class DeleteAiModelEndpoint(IMediator mediator) : EndpointWithoutRequest<
     public override void Configure()
     {
         Delete("/ai/models/{Id}");
-        AllowAnonymous();
+        Permissions("ai-model:write");
     }
 
     public override async Task HandleAsync(CancellationToken ct)
@@ -84,7 +83,7 @@ public class SetDefaultAiModelEndpoint(IMediator mediator) : EndpointWithoutRequ
     public override void Configure()
     {
         Post("/ai/models/{Id}/default");
-        AllowAnonymous();
+        Permissions("ai-model:write");
     }
 
     public override async Task HandleAsync(CancellationToken ct)

src/BuildFlow.Host/Endpoints/rag/RAG/RAGStreamEndpoint.cs

@@ -1,6 +1,5 @@
 using System.Text;
 using System.Text.Json;
-using Microsoft.Extensions.AI;
 using BuildFlow.Application.RagQA.DTOs;
 using BuildFlow.Domain.Interfaces;
 using BuildFlow.Infrastructure.Persistence;
@@ -24,7 +23,7 @@ public class RAGStreamEndpoint(
     public override void Configure()
     {
         Post("/rag/stream");
-        AllowAnonymous();
+        Permissions("rag:query");
     }
 
     public override async Task HandleAsync(RAGQueryRequest req, CancellationToken ct)