feat(client): 新增会话管理与消息落库能力

补齐客户端会话生命周期接口（创建、列表、消息分页、改名、删除），并在流式 chat 中强制绑定 sessionId 与落库消息，确保会话标题和历史可追踪，同时统一 Swagger 文档为 DTO 驱动以减少重复维护。

Made-with: Cursor

prisma/migrations/20260422180000_add_chat_sessions_messages/migration.sql

@@ -0,0 +1,35 @@
+-- CreateTable
+CREATE TABLE "chat_sessions" (
+    "id" BIGSERIAL NOT NULL,
+    "user_id" BIGINT NOT NULL,
+    "title" VARCHAR(200),
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updated_at" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "chat_sessions_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "chat_messages" (
+    "id" BIGSERIAL NOT NULL,
+    "session_id" BIGINT NOT NULL,
+    "role" VARCHAR(20) NOT NULL,
+    "content" TEXT NOT NULL,
+    "token_count" INTEGER NOT NULL DEFAULT 0,
+    "provider" VARCHAR(64),
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "chat_messages_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "chat_sessions_user_id_idx" ON "chat_sessions"("user_id");
+
+-- CreateIndex
+CREATE INDEX "chat_messages_session_id_idx" ON "chat_messages"("session_id");
+
+-- AddForeignKey
+ALTER TABLE "chat_sessions" ADD CONSTRAINT "chat_sessions_user_id_fkey" FOREIGN KEY ("user_id") REFERENCES "users"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "chat_messages" ADD CONSTRAINT "chat_messages_session_id_fkey" FOREIGN KEY ("session_id") REFERENCES "chat_sessions"("id") ON DELETE CASCADE ON UPDATE CASCADE;

prisma/schema.prisma

@@ -15,5 +15,34 @@ model User {
   createdAt DateTime @default(now()) @map("created_at")
   updatedAt DateTime @updatedAt @map("updated_at")
 
+  sessions ChatSession[]
+
   @@map("users")
 }
+
+model ChatSession {
+  id        BigInt   @id @default(autoincrement())
+  userId    BigInt   @map("user_id")
+  user      User     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  title     String?  @db.VarChar(200)
+  messages  ChatMessage[]
+  createdAt DateTime @default(now()) @map("created_at")
+  updatedAt DateTime @updatedAt @map("updated_at")
+
+  @@index([userId])
+  @@map("chat_sessions")
+}
+
+model ChatMessage {
+  id          BigInt      @id @default(autoincrement())
+  sessionId   BigInt      @map("session_id")
+  session     ChatSession @relation(fields: [sessionId], references: [id], onDelete: Cascade)
+  role        String      @db.VarChar(20)
+  content     String      @db.Text
+  tokenCount  Int         @default(0) @map("token_count")
+  provider    String?     @db.VarChar(64)
+  createdAt   DateTime    @default(now()) @map("created_at")
+
+  @@index([sessionId])
+  @@map("chat_messages")
+}