refactor: 将 n8n 工作流外部化并简化数据库 schema

- 移除 n8n-workflows 目录下的工作流配置文件
- 从 Project 模型移除 embedding 和 embeddingUpdatedAt 字段
- 添加 N8N_AI_SEARCH_WEBHOOK 环境变量配置

Co-Authored-By: Claude (glm-4.7) <noreply@anthropic.com>

prisma/schema.prisma

@@ -39,25 +39,23 @@ enum TaskStatus {
 // ================================
 
 model Project {
-  id                String        @id @default(cuid())
-  name              String
-  nameEn            String?
-  slug              String        @unique
-  description       String
-  descriptionEn     String?
-  content           String?       @db.Text
-  contentEn         String?       @db.Text
-  status            ProjectStatus @default(ACTIVE)
-  source            String?
-  embedding         Unsupported("vector(1536)")?
-  embeddingUpdatedAt DateTime?
-  createdAt         DateTime      @default(now())
-  updatedAt         DateTime      @updatedAt
+  id             String        @id @default(cuid())
+  name           String
+  nameEn         String?
+  slug           String        @unique
+  description    String
+  descriptionEn  String?
+  content        String?       @db.Text
+  contentEn      String?       @db.Text
+  status         ProjectStatus @default(ACTIVE)
+  source         String?
+  createdAt      DateTime      @default(now())
+  updatedAt      DateTime      @updatedAt
 
   // Relations
-  tags              ProjectTag[]
-  links             ExternalLink[]
-  discoveryTasks    ProjectDiscoveryTask[]
+  tags           ProjectTag[]
+  links          ExternalLink[]
+  discoveryTasks ProjectDiscoveryTask[]
 
   // Indexes
   @@index([status, createdAt], map: "idx_project_status_createdAt")