feat(admin): Implement System Knowledge Base management module

Features:

- Backend: SystemKbService with full CRUD (knowledge bases + documents)

- Backend: 8 RESTful API endpoints (list/detail/create/update/delete/upload/download)

- Backend: OSS storage integration (system/knowledge-bases/{kbId}/{docId})

- Backend: RAG engine integration (document parsing, chunking, vectorization)

- Frontend: SystemKbListPage with card-based layout

- Frontend: SystemKbDetailPage with document management table

- Frontend: Master-Detail UX pattern for better user experience

- Document upload (single/batch), download (preserving original filename), delete

Technical:

- Database migration for system_knowledge_bases and system_kb_documents tables

- OSSAdapter.getSignedUrl with Content-Disposition for original filename

- Reuse RAG engine from common/rag for document processing

Tested: Local environment verified, all features working

backend/prisma/schema.prisma

@@ -1265,12 +1265,13 @@ enum VerificationType {
 
 /// Prompt模板 - 存储Prompt的元信息
 model prompt_templates {
-  id          Int               @id @default(autoincrement())
-  code        String            @unique /// 唯一标识符，如 'RVW_EDITORIAL'
-  name        String            /// 人类可读名称，如 "稿约规范性评估"
-  module      String            /// 所属模块: RVW, ASL, DC, IIT, PKB, AIA
-  description String?           /// 描述
-  variables   Json?             /// 预期变量列表，如 ["title", "abstract"]
+  id               Int               @id @default(autoincrement())
+  code             String            @unique /// 唯一标识符，如 'RVW_EDITORIAL'
+  name             String            /// 人类可读名称，如 "稿约规范性评估"
+  module           String            /// 所属模块: RVW, ASL, DC, IIT, PKB, AIA
+  description      String?           /// 描述
+  variables        Json?             /// 预期变量列表，如 ["title", "abstract"]
+  knowledge_config Json?             @map("knowledge_config") /// 知识库增强配置
   
   versions    prompt_versions[]
   
@@ -1312,6 +1313,52 @@ enum PromptStatus {
   @@schema("capability_schema")
 }
 
+/// 系统知识库 - 运营管理的公共知识库，供 Prompt 引用
+model system_knowledge_bases {
+  id             String                  @id @default(uuid())
+  code           String                  @unique @db.VarChar(50) /// 唯一编码，如 'CONSORT_2010'
+  name           String                  @db.VarChar(100) /// 名称，如 'CONSORT 2010 声明'
+  description    String?                 @db.Text /// 描述
+  category       String?                 @db.VarChar(50) /// 分类: methodology, statistics, crf
+  document_count Int                     @default(0) @map("document_count") /// 文档数量
+  total_tokens   Int                     @default(0) @map("total_tokens") /// 总 Token 数
+  status         String                  @default("active") @db.VarChar(20) /// 状态: active, archived
+  
+  documents      system_kb_documents[]
+  
+  created_at     DateTime                @default(now()) @map("created_at")
+  updated_at     DateTime                @updatedAt @map("updated_at")
+
+  @@index([category], map: "idx_system_kb_category")
+  @@index([status], map: "idx_system_kb_status")
+  @@map("system_knowledge_bases")
+  @@schema("capability_schema")
+}
+
+/// 系统知识库文档 - 知识库中的文档
+model system_kb_documents {
+  id            String                 @id @default(uuid())
+  kb_id         String                 @map("kb_id") /// 所属知识库ID
+  filename      String                 @db.VarChar(255) /// 原始文件名
+  file_path     String?                @db.VarChar(500) @map("file_path") /// OSS 存储路径
+  file_size     Int?                   @map("file_size") /// 文件大小(字节)
+  file_type     String?                @db.VarChar(50) @map("file_type") /// 文件类型: pdf, docx, md, txt
+  content       String?                @db.Text /// 解析后的文本内容
+  token_count   Int                    @default(0) @map("token_count") /// Token 数量
+  status        String                 @default("pending") @db.VarChar(20) /// 状态: pending, processing, ready, failed
+  error_message String?                @db.Text @map("error_message") /// 错误信息
+  
+  knowledge_base system_knowledge_bases @relation(fields: [kb_id], references: [id], onDelete: Cascade)
+  
+  created_at    DateTime               @default(now()) @map("created_at")
+  updated_at    DateTime               @updatedAt @map("updated_at")
+
+  @@index([kb_id], map: "idx_system_kb_docs_kb_id")
+  @@index([status], map: "idx_system_kb_docs_status")
+  @@map("system_kb_documents")
+  @@schema("capability_schema")
+}
+
 // ============================================================
 // EKB Schema - 知识库引擎 (Enterprise Knowledge Base)
 // 参考文档: docs/02-通用能力层/03-RAG引擎/04-数据模型设计.md